Photosensitive reducible silver ion-containing compositions

ABSTRACT

A photosensitive reducible silver ion-containing composition can be used to provide electrically-conductive silver metal in thin films or patterns. This composition comprises: a) a non-hydroxylic-solvent soluble silver complex represented by the following formula (I): 
       (Ag + ) a (L) b (P) c    (I)
 
     wherein L represents an α-oxy carboxylate; P represents a 5- or 6-membered N-heteroaromatic compound; a is 1 or 2; b is 1 or 2; and c is 1, 2, 3, or 4, provided that when a is 1, b is 1, and when a is 2, b is 2; b) optionally, a photosensitizer that can either reduce the reducible silver ion or oxidize the α-oxy carboxylate; and c) a solvent medium comprising at least one non-hydroxylic solvent. Electrically-conductive silver can be provided by photochemical conversion of the reducible silver ions in the complex.

RELATED APPLICATIONS

Reference is made to the following commonly assigned and copendingpatent application, the disclosures of all of which are incorporatedherein by reference:

U.S. Ser. No. 15/______ (filed on even date herewith by Shukla) andentitled “Silver Ion Carboxylate N-heteroaromatic Complexes” (AttorneyDocket K002092/JLT);

U.S. Ser. No. 15/______ (filed on even date herewith by Shukla, Lenhard,Mis, and Donovan) and entitled “Methods for Forming and Using SilverMetal” (Attorney Docket K002108/JLT);

U.S. Ser. No. 15/______ (filed on even date herewith by Shukla, Mis,Welter, Klubek, and Donovan) and entitled “Articles Having ReducibleSilver Ion Complexes or Silver Metal” (Attorney Docket K002109/JLT);

U.S. Ser. No. 15/______ (filed on even date herewith by Shukla) andentitled “Silver Ion Carboxylate Primary Alkylamine Complexes” (AttorneyDocket K002110/JLT);

U.S. Ser. No. 15/______ (filed on even date herewith by Shukla) andentitled “Photosensitive Reducible Silver Ion-Containing Compositions”(Attorney Docket K002111/JLT);

U.S. Ser. No. 15/______ (filed on even date herewith by Shukla, Lenhard,Mis, and Donovan) and entitled “Methods for Forming and Using SilverMetal” (Attorney Docket K002112/JLT); and

U.S. Ser. No. 15/______ (filed on even date herewith by Shukla, Mis,Welter, and Donovan) and entitled “Articles with Reducible Silver Ionsor Silver Metal” (Attorney Docket K002113/JLT).

FIELD OF THE INVENTION

This invention relates to photosensitive reducible silver ion-containingcompositions that can be used to provide electrically-conductive silvermetal in thin film coatings or patterns on various substrates. Suchphotosensitive compositions can include a photosensitizer and anon-hydroxylic-solvent soluble silver complex that can provide silvermetal upon suitable irradiation. Each complex includes a reduciblesilver ion complexed with both an α-oxy carboxylate and a 5- or6-membered N-heteroaromatic compound.

BACKGROUND OF THE INVENTION

It is well known that silver as a precious metal has desirableelectrical and thermal conductivity, catalytic properties, andantimicrobial behavior. Thus, silver and silver-containing compoundshave been widely used in alloys, metal plating processes, electronicdevices, imaging sciences, medicine, clothing or other fibrousmaterials, and other commercial and industrial articles and processes totake advantage of silver's beneficial properties.

For example, silver compounds or silver metal have been described foruse as metallic patterns or electrodes in metal wiring patterns, printedcircuit boards (PCB's), flexible printed circuit boards (FPC's),antennas for radio frequency identification (RFID) tags, plasma displaypanels (PDP's), liquid crystal displays (LCD's), organic light emittingdiodes (OLED's), flexible displays and organic thin film transistors(OTFT's), among other electronic devices known in the art.

Rapid advances are also occurring for making and using variouselectronic devices for various communication, financial, and archivalpurposes.

Silver is an ideal conductor having electrical conductivity 50 to 100times greater than indium tin oxide that is commonly used today in manydevices. For example, the art has described the preparation ofelectrically-conductive films by forming and developing (reducing) asilver halide image in “photographic” silver halide emulsions through anappropriate mask to form of electrically-conductive grid networks havingsilver wires having average sizes (width and height) of less than 10 μmand having appropriate lengths. Various efforts have been made to designthe silver halide emulsions and processing conditions to optimizeelectrically-conductive grid designs.

While silver as an electrical conductor has a wide range of potentialuses in the field of printed electronics, the microfabrication ofelectrically-conductive tracks (grids, wires, or patterns) byphotolithographic and electroless techniques is time consuming andexpensive, and there is an industrial need for direct digital printingto simplify the processes and to reduce manufacturing costs.

Furthermore, it is desirable to fabricate silver-containing electronicsonto polymeric or similar temperature-sensitive substrates bysolution-based printing processes. Metallic electrically-conductivewires or grids of low resistance must be achieved at sufficiently lowtemperatures so as to be compatible with organic electronics onpolymeric substrates. Among various known methods for fabricatingelectrically-conductive silver grids or patterns, the direct printing ofsilver-containing inks provides attractive prospects for making suchelectrically-conductive patterns.

Commonly used silver-conductive inks useful for this purpose arecurrently based or dependent upon the presence of silver nanoparticle(NP) solutions or dispersions, all of which have associated drawbacks.To overcome the common problem of aggregation and flocculation in silvernanoparticle based inks, various thiolate encapsulating surfactants ordispersants can be used. Volkman et al. [Chem. Mater. 23, 4634-4640(2011)] observed that a thiolate encapsulating surfactant could be usedto treat 3 nm silver particles in silver-containing inks to achievefilms sintered at temperatures above 175° C. in air. Sintering isessential to obtain the electrical conductivities required forelectronic applications. The effects of sintering on electricalperformance and microstructure for an inkjet-printed copper nanoparticleink were explored by Niittynen et al. [Sci. Rep. 5, article number: 8832(2015)]. These workers used laser and intense pulsed light (IPL)sintering in order to obtain articles having electrical conductivitiesgreater than 20% of that of bulk copper.

However, sintering techniques have major disadvantages. In many cases,sintering steps require high temperatures that are not compatible withpolymer substrates such as polyethylene terephthalate or polycarbonatethat are commonly employed in many consumer electronic articles.Furthermore, the metal-containing inks used for these processes havedisparate viscosities and synthetic parameters. Particle-based inkstypically contain electrically-conductive metal particles that aresynthesized separately and then incorporated into an ink formulation.Each resulting particle-based ink must then be optimized for use in aspecific printing process.

Grouchko et al. [ACS Nano 5(4) 3354-3359 (2011)] recently overcame someof these problems by employing a room temperature, “built in” sinteringmechanism that successfully produced silver metal articles exhibitingelectrical conductivities as high as 41% of the electrical conductivityof bulk silver. To obtain these electrical conductivity values, achloride salt (such as NaCl) or HCl vapor was employed to strip apolymeric (polyacrylic acid sodium salt) electrosterically stabilizingcoating from the ˜15 nm diameter silver nanoparticle feedstock. Thissintering mechanism consisted of spontaneous coalescence and Ostwaldripening, driven by the surface-to-volume energy of the very smallsilver nanoparticles. Thus, all of these nanoparticle-based processesinherently involve sintering processes, whether they are chemical (forexample using a strong acid such as hydrochloric acid), thermal, laser,or UV activated.

Inkjet printing and flexographic printing have also been proposed forproviding patterns of silver or silver-containing compounds, requiringthe careful fabrication of a silver-containing paste or “ink” withdesirable surface tension, viscosity, stability, and other physicalproperties required for such application processes. High silver contenthas generally been required for high electrical conductivity, andcalcination or sintering may be additionally required for increasingelectrical conductivity of printed silver inks.

An alternative to the approaches described above is to employ a chemicalink formulation where the silver source is a molecular precursor orcation (such as a silver salt) that is then chemically reacted (orreduced) to produce silver metal. Electrically-conductive inks that arein the form of a chemical solution rather than as a suspension ordispersion of metal particles, have gained interest in recent years [seefor example Walker and Lewis in J. Am. Chem. Soc. 134, 1419 (2012); andJahn et al. Chem. Mater. 22, 3067-3071 (2010)]. One conductive ink ofthis type is known as a Metalorganic Decomposition (MOD) variety ink,for example, as described by Jahn et al. [Chem. Mater. 22, 3067-3071(2010)] who investigated silver printing using an aqueous transitionmetal complex [AgO₂C(CH₂OCH₂)₃H]-containing MOD ink. They reported theformation of metallic silver features having electrical conductivitiesas high as 2.7×10⁷ S m⁻¹, which corresponds to an electricalconductivity that is 43% of that of bulk silver, although a sinteringtemperature of 250° C. was required. MOD inks thus overcome someproblems associated with the use of nanoparticle-containing inks, forexample, nozzle clogging, but numerous printing passes are generallyrequired to obtain an adequate sheet resistance. Post-treatmentsintering processes are also still required to fully consolidate theelectrically-conductive articles if the growth process is initiated fromdiscrete nanoparticle intermediates which is common in MOD inkprocesses.

U.S. Patent Application Publication 2015-0004325 (Walker et al.)describes a chemically-reactive silver ink composition comprised of acomplex of a silver carboxylate salt and an alkylamine, in which thecomplex is used to form an electrically-conductive silver structure at atemperature of 120° C. or less. Unfortunately, even these temperaturesrender the ink incompatible with many polymeric and paper substratesused in flexible electronic and biomedical devices. Furthermore, sincealkylamines are known to reduce silver at room temperature, long termstability of such compositions is tentative. The complexes must be keptin air-tight refrigerated storage for extended keeping stability (ColumnI, paragraph 0054 of the publication). Furthermore, the publicationteaches long heating times were needed to obtain low resistivity in theresulting articles.

A common coordinating ion to form organic silver complexes is carboxylicacid [Prog. Inorg. Chem., 10, 233 (1968)]. However, silver-carboxylatecomplexes are generally insoluble in organic solvents [see for example,U.S. Pat. No. 5,491,059 of Whitcomb and U.S. Pat. No. 5,534,312 of Hillet al.] and have a high decomposition temperature. To solve thisproblem, several methods have been proposed for example, in Ang. Chem.,Int. Ed. Engl., 31, p. 770 (1992), Chem. Vapor Deposition, 7, 111(2001), Chem. Mater., 16, 2021 (2004), and U.S. Pat. No. 5,705,661(Iwakura et al.). Among such methods are those using silver carboxylateshaving long alkyl chains or including amine compounds or phosphinecompounds. However, the silver complexes known thus far haveinsufficient stability or solubility and a high decompositiontemperature is needed for pattern formation and are decomposed slowly.

Allegedly to address some of these problems, U.S. Pat. No. 8,226,755(Chung et al.) describes silver complexes formed by reacting a silvercompound (such as a silver salt) with an ammonium carbamate compound orammonium carbonate compound. Moreover, U.S. Patent ApplicationPublication 2010/0021704 (Yoon et al.) describes the preparation and useof fatty acid silver salts complexed with amines and in admixture withsilver oxide to form silver metal from the silver oxide at lowtemperature.

U.S. Pat. No. 8,163,073 (Chan et al.) describes the use of silverammonium complex ions, silver amine complex ions, silver-amino acidcomplex ions, silver halide complex ions, silver sulfite complex ions,or silver thiosulfate complex ions for silver plating processes to formsilver wires for various devices.

U.S. Pat. No. 7,682,774 (Kim et al.) describes other photosensitivecompositions comprising silver fluoride-organic complex precursors ascatalyst precursors as well as the use of polymer derived from a monomerhaving a carboxyl group and a co-polymerizable monomer that may providepolymeric stability and developability of the resulting “seed” silvercatalyst particles used for electroless plating.

U.S. Pat. No. 8,419,822 (Li) describes a process for producingcarboxylic acid-stabilized silver nanoparticles by heating a mixture ofa silver salt, a carboxylic acid, and a tertiary amine. However, it hasbeen observed that such silver-containing complexes are not thermally orlight stable. The reducible silver ions are readily reduced underambient light conditions, and the resulting electrical conductivity ofsilver particles is minimal.

Other industrial approaches to preparing electrically-conductive filmsor elements have been directed to formulating and applying photocurablecompositions containing dispersions of metal particles such as silvermetal particles to substrates, followed by curing of the photocurablecomponents in the photocurable compositions. The applied silverparticles in the cured compositions thus act as catalytic (seed)particles for electrolessly plated electrically-conductive metals.Useful electrically-conductive grids prepared in this manner aredescribed for example, in U.S. Pat. No. 9,188,861 (Shukla et al.) andU.S. Pat. No. 9,207,533 (Shukla et al.) and in US Patent ApplicationPublications 2014/0071356 (Petcavich) and 2015/0125596 (Ramakrishnan etal.). Using these methods, photocurable compositions containingcatalytic silver particles can be printed and cured on a suitabletransparent substrate, for example a continuous roll of a transparentpolyester, and then electroless plating can be carried out on thecatalytic silver particles. However, these methods require that highquantities of silver particles be dispersed within the photocurablecompositions in a uniform manner so that coatings or printed patternshave sufficiently high concentration of catalytic sites. Withouteffective dispersing, silver particles readily agglomerate, leading toless effective and uniform application of catalytic metal patterns andelectroless plating.

Despite all of the various approaches and efforts to provideelectrically-conductive silver in various consumer and industrialarticles described above, there remains a need for photosensitivesilver-generating compositions and processes which can rapidly generatemetallic silver at room temperature. Ideally such photosensitivecompositions should have several properties: stability at roomtemperature for an extended period of time (limited self-reduction ofsilver ions); capable of being deposited using a wide range ofapplication processes, whether uniformly or patternwise; useful at roomtemperature; and controllable chemical activity.

SUMMARY OF THE INVENTION

The present invention provides a photosensitive reducible silverion-containing composition comprising:

a) a non-hydroxylic-solvent soluble silver complex comprising areducible silver ion complexed with an α-oxy carboxylate and a 5- or6-membered N-heteroaromatic compound,

the non-hydroxylic-solvent soluble silver complex being represented bythe following formula (I):

(Ag⁺)_(a)(L)_(b)(P)_(c)   (I)

wherein L represents the α-oxy carboxylate; P represents the 5- or6-membered N-heteroaromatic compound; a is 1 or 2; b is 1 or 2; and c is1, 2, 3, or 4, provided that when a is 1, b is 1, and when a is 2, b is2;

b) optionally, a photosensitizer that can either reduce the reduciblesilver ion or oxidize the α-oxy carboxylate; and

c) a solvent medium comprising at least one non-hydroxylic solvent.

The present invention is directed to novel non-hydroxylic-solventsoluble silver complexes, each complex comprising a silver ion complexedwith one or more α-oxy carboxylate compounds and one or more 5- or6-membered N-heteroaromatic compounds, and to uses of such complexes inphotosensitive compositions and articles, and methods for producing andusing same. For example, such novel complexes can be incorporated intosilver “inks” or photosensitive reducible silver ion-containingcompositions that can include a photosensitizer and a solvent mediumcomprising one or more non-hydroxylic solvents. When present, thephotosensitizer upon absorption of actinic radiation, decomposes thenon-hydroxylic-solvent soluble silver complex to formelectrically-conductive metallic silver in a rapid manner at roomtemperature. Reducible silver ions can be photochemically converted tosilver metal without the photosensitizer being present but this usuallyhappens at a significantly slower rate.

Such novel complexes described herein and photosensitive compositionscontaining same can be used in various methods comprising the silver“ink” as a uniform photosensitive thin film or as a photosensitive thinfilm pattern on a substrate, and exposing the applied material tosuitable actinic radiation to generate electrically-conductive silvermetal (uniform layer or pattern) at room temperature.

The present invention provides several important advantages over knowntechnology.

Firstly, in the presence of an appropriate photosensitizer, uponabsorption of actinic radiation the non-hydroxylic solvent-solublesilver complex according to the present invention herein rapidlygenerates electrically-conductive silver metal at room temperature.Thus, metallic silver generation is possible in a high speed, continuousmanufacturing operations, such as roll-to-roll operations.

In addition, the complexes described herein and the photosensitivecompositions into which they are incorporated according to thisinvention, are stable at room temperature when kept in the dark or underyellow safe light conditions so that there is very little prematurereduction of silver ion. Thus, the chemistry according to the presentinvention in such complexes and photosensitive compositions is highlycontrollable so that they do not prematurely degrade and can be used ina wide variety of operations.

Since metallic silver is generated at room temperature upon exposure toactinic radiation, the photosensitive compositions according to thepresent invention provide greater flexibility in choice of substrateused including plastics (polymers), metals, glass, and other materialsthat could be used in various end products or electronic devices.

Moreover, as the photosensitive compositions according to the presentinvention are generally in the form of clear liquids, it is possible tochoose a wide array of deposition techniques when producing variousarticles and uses, including but not limited to flexographic printing,ink jet printing, screen printing, gravure printing, roll-to-rollcoating, spraying, and other techniques that would be readily apparentto one skilled in the art.

The advantages described herein are achieved with the use of novelnon-hydroxylic-solvent soluble silver complexes described herein. Eachcomplex comprises at least one reducible silver ion that is complexedwith an α-oxy carboxylate and a 5- or 6-membered N-heteroaromaticcompounds. These non-hydroxylic-solvent soluble silver complexes aredescribed in more detail below.

The provision of silver metal from the complexes according to thepresent invention can be carried out in one of two differentphotochemical processes, depending upon the type of photosensitizer thatis present. In some embodiments, the photosensitizer iselectron-accepting and upon excitation with photon captured fromelectromagnetic radiation, it reacts with the α-oxy carboxylate ion, butin other embodiments, the photosensitizer is electron-donating and uponexcitation with photon captured from electromagnetic radiation, itreacts with the reducible silver ion.

Other advantages of the present invention would be readily apparent toone skilled in the art in view of the teaching provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the crystal structure of a silverion-containing complex as described in Invention Example 1 below.

FIG. 2 is an illustration of the crystal structure of a silverion-containing complex as described in Invention Example 2 below.

FIG. 3 is an illustration of the crystal structure of a silverion-containing complex as described in Invention Example 6 below.

FIG. 4 is a graphical representation of a typical cyclic voltammogram ofa silver ion-containing complex as described in Inventive Example 11below.

DETAILED DESCRIPTION OF THE INVENTION

The following discussion is directed to various embodiments of thepresent invention and while some embodiments can be desirable forspecific uses, the disclosed embodiments should not be interpreted orotherwise considered to limit the scope of the present invention, asclaimed below. In addition, one skilled in the art will understand thatthe following disclosure has broader application than is explicitlydescribed in the discussion of any embodiment.

Definitions

As used herein to define various components of the photosensitivereducible silver ion-containing compositions, photosensitive thin films,photosensitive thin film patterns, or other materials used in thepractice of the present invention, unless otherwise indicated, thesingular forms “a,” “an,” and “the” are intended to include one or moreof the components (that is, including plurality referents).

Each term that is not explicitly defined in the present application isto be understood to have a meaning that is commonly accepted by thoseskilled in the art. If the construction of a term would render itmeaningless or essentially meaningless in its context, the term shouldbe interpreted to have a standard dictionary meaning.

The use of numerical values in the various ranges specified herein,unless otherwise expressly indicated otherwise, are considered to beapproximations as though the minimum and maximum values within thestated ranges were both preceded by the word “about.” In this manner,slight variations above and below the stated ranges may be useful toachieve substantially the same results as the values within the ranges.In addition, the disclosure of these ranges is intended as a continuousrange including every value between the minimum and maximum values aswell as the end points of the ranges.

Unless otherwise indicated, the term “weight %” refers to the amount ofa component or material based on the total amount of a photosensitivereducible silver ion-containing composition, formulation, solution. Inother embodiments, “weight %” can refer to the % solids (or dry weight)of a dry layer, coating, thin film, silver wire, or silver pattern.

Unless otherwise indicated herein, the terms “non-hydroxylic-solventsoluble silver complex,” “silver ion-containing complex,” and “complex”refer to embodiments according to the present invention.

Unless otherwise indicated herein, the terms “photosensitivecomposition” and “photosensitive reducible silver ion-containingcomposition” refer to embodiments according to the present invention.

Unless otherwise indicated herein, “photosensitivity” refers to theability for silver ions to be reduced to silver metal in a complex orphotosensitive composition when irradiated with ultraviolet (UV) orvisible radiation within the range of wavelengths of at least 150 nm andup to and including 750 nm, or particularly at least 190 nm and up toand including 450 nm. Thus, photosensitivity refers to either thecomplex directly absorbing radiation and undergoing photochemicalreaction, or to a photosensitizer in the photosensitive compositionabsorbing actinic radiation and transferring energy to the complex viaelectron transfer to initiate the desired reaction.

Unless otherwise indicated, the term “non-aqueous” as applied to thephotosensitive reducible silver ion-containing composition or solutionsmeans that solvent media used to form such compositions or solutions arepredominantly organic in nature and water is not purposely added but maybe present in an amount of less than 10 weight %, or particularly lessthan 5 weight %, or even less than 1 weight %, of the total weight ofall solvents in the solvent medium.

Average dry thickness of photosensitive thin films and silvermetal-containing thin films described herein can be the average of atleast 2 separate measurements taken, for example, using electronmicroscopy, optical microscopy, or profilometry.

Similarly, the average dry thickness or width of silver metal (includingsilver) lines, grid lines, or other silver metal-containing thin filmpattern features described herein can be the average of at least 2separate measurements taken, for example, using electron microscopy,optical microscopy, or profilometry.

The use of “dry” in reference to thickness and width refers toembodiments in which at least 50 weight % of originally presentsolvent(s) has been removed.

Unless otherwise indicated, the term “group” particularly when used todefine a substituent or a moiety, can itself be substituted orunsubstituted (for example an “alkyl group” refers to a substituted orunsubstituted alkyl group) by replacement of one or more hydrogen atomswith suitable substituents (noted below) such as a fluorine atom.Generally, unless otherwise specifically stated, substituents on any“groups” referenced herein or where something is stated to be possiblysubstituted, include the possibility of any groups, whether substitutedor unsubstituted, which do not destroy properties necessary for theutility of the component or non-aqueous metal catalytic composition. Itwill also be understood for this disclosure and claims that reference toa compound or complex of a particular general structure includes thosecompounds of other more specific formula that fall within the generalstructural definition. Examples of substituents on any of the mentionedgroups can include known substituents such as: halogen (for example,chloro and fluoro); alkoxy, particularly those with 1 to 5 carbon atoms(for example, methoxy and ethoxy); substituted or unsubstituted alkylgroups, particularly lower alkyl groups (for example, methyl andtrifluoromethyl), particularly either of those having 1 to 6 carbonatoms (for example, methyl, ethyl, and t-butyl); and other substituentsthat would be readily apparent in the art.

Unless otherwise indicated, all voltages described herein are measuredversus SCE (saturated calomel electrode).

The term “non-hydroxylic” as used to define organic solvents used in thepractice of the present invention refers to organic solvents from whichhydroxy groups (—OH) are completely absent. Such non-hydroxylic solventsdo not include water.

A protic solvent is a solvent that has a hydrogen atom bound to anoxygen atom (as in a hydroxyl group) or to a nitrogen atom (as in anamine group).

Uses

The deposition or patterning of functional electrodes, pixel pads, andconductive traces, lines and tracks, which meet electrical conductivity,processing, and cost requirements for practical applications have been agreat challenge. Silver metal is of particular interest inelectrically-conductive elements for electronic devices because silveris much lower in cost than gold and it possesses much betterenvironmental stability than copper.

The inventive compositions of the present invention can be used forforming electrically-conductive metallic silver patterns and electrodesfor example in membrane touch switches (MTS), battery testers,biomedical, electroluminescent lamps, radio frequency identification(RFID) antenna, flat panel displays such as plasma display panel (PDP)and organic light emitting diode (OLED) displays, printed transistorsand thin film photovoltaics, and thereby reduce the numbers of steps forpattern formation in such devices.

The non-hydroxylic-solvent soluble silver complexes described hereinhave a number of actual and potential uses in various technologies andindustries. Most specifically, they can be used to provide silver metalfor various purposes, including but not limited to, the formation ofelectrically-conductive grids or patterns of fine wires or othergeometric forms, the formation of silver seed particles for electrolessplating with other electrically-conductive metals, and the formation ofsilver in various materials for antimicrobial activity.

More specifically, the non-hydroxylic-solvent soluble silver complexesdescribed herein are particularly useful as part of photosensitivereducible silver ion-containing compositions that can be irradiated withUV or visible radiation of a chosen wavelength to provide silver metalas part of electrically-conductive metal patterns. Theseelectrically-conductive metal patterns can be incorporated into variousdevices including but not limited to, touch screens or other transparentdisplay devices, and in modern electronics such as solar cellelectrodes, electrodes in organic thin film transistors (OTFTs),flexible displays, radio frequency identification tags, light antennas,and other devices that would be readily apparent to one skilled in theart from the teaching herein.

While it is not necessary to achieve exceptional advantages from use ofthe present invention, silver metal formed according to the presentinvention can also be used as catalytic sites for electrochemicalplating using silver or other metals to improveelectrically-conductivity of the resulting metal thin films or patterns.

Non-Hydroxylic-Solvent Soluble Silver Complexes

The inventive non-hydroxylic-solvent soluble silver complexes aredesigned with only three essential components: (1) one or two reduciblesilver ions complexed with both (2) one or two α-oxy carboxylatemolecules, and (3) one, two, three, or four 5- or 6-memberedN-heteroaromatic compound molecules, all of which components aredescribed below.

In general, each useful non-hydroxylic-solvent soluble silver complexcan be represented by the following formula (I):

(Ag⁺)_(a)(L)_(b)(P)_(c)   (I)

wherein L represents the α-oxy carboxylate; P represents the 5- or6-membered N-heteroaromatic compound; a is 1 or 2; b is 1 or 2; and c is1, 2, 3, or 4, provided that when a is 1, b is 1, and when a is 2, b is2.

In some embodiments:

(i) a and b are both 1 and c is 1 or 2;

(ii) a and b are both 2 and c is 2; or

(iii) a and b are both 2 and c is 4.

In addition, each non-hydroxylic-solvent soluble silver complexaccording to the present invention, has at minimum solubility in anon-hydroxylic solvent (as defined below) or at least 5 g/liter atatmospheric pressure and ambient temperature (15° C. to 25° C.). It isparticular useful that this solubility feature is true in acetonitrilethat is one of the more useful non-hydroxylic solvents.

In general, each non-hydroxylic-solvent soluble silver complex offormula (I) can be defined using oxidation potentials determinedseparately for the component parts, such that the “P” component that is5- or 6-membered N-heteroaromatic compound having an oxidation potentialof at least 1.0 V, at least 1.5 V, or even at least 2.0 V vs. SCE; the“L” component, that is, the α-oxy carboxylate, has a first oxidationpotential of at least 1.0 V vs. SCE; and upon decarboxylation of theα-oxy carboxylate, a second radical is generated that has an oxidationpotential of less than 1.0 V vs. SCE.

More specifically, the 5- or 6-membered N-heteroaromatic compound has anoxidation potential of greater than 1.5 V vs. SCE.

Further details of such properties are provided below.

It is very important that the non-hydroxylic-solvent soluble silvercomplexes according to this invention have significant stability overtime in that each complex meets a silver ion stability test such thatwhen the non-hydroxylic-solvent soluble silver complex is kept for 24hours at ambient temperature (15-25° C.) and under yellow safelight,less than 0.1 mol % of the original silver ion content in the complex isreduced to silver metal (as tested by chemical analysis and UV-Visabsorption spectroscopy).

Silver (Ag) Ions:

Each of the non-hydroxylic-solvent soluble silver complexes according tothe present invention comprises one or two reducible silver ions, thatis, one or two Ag⁺ or Ag⁺¹ ions, as a first essential component. Eachreducible silver ion is complexed with one or two α-oxy carboxylatecompounds. The complexation with an α-oxy carboxylate compound could bevia two oxygen atoms provided from the same molecule of an α-oxycarboxylate compound, or oxygen atoms provided from two molecules of thesame or different α-oxy carboxylate compounds.

In general, each non-hydroxylic-solvent soluble silver complex offormula (I) shown above can be defined using reduction potentials suchthat the Ag⁺¹ ion of the complex can have a reduction potential of lessthan 1.0 V vs. SCE; or the Ag⁺¹ ion of the complex can have a reductionpotential of less than 0.5 V vs. SCE; or the Ag⁺¹ ion of the complex canhave a reduction potential of less than 0 V vs. SCE.

Silver ions can be provided using any suitable silver salt, and asdescribed below, they can be provided as part of a silver carboxylatesalt in which the carboxylate is an α-oxy carboxylate [L component informula (I)] according to the present invention.

α-Oxy Carboxylates:

A second essential component of the non-hydroxylic solvent-solublecomplexes according to this invention includes one or more α-oxycarboxylate groups (moieties or components) in which the α-carbon atomattached directly to the carboxyl group [—C(═O)O-] has a hydroxy group,oxy, or an oxyalkyl substituent group. Thus, the α-oxy carboxylates canbe either α-hydroxy carboxylates, α-alkoxy carboxylates, or α-oxycarboxylates. With the α-hydroxy carboxylates and α-alkoxy carboxylates,the remainder of the valences of that α-carbon atom can be filled withhydrogen or a branched or linear alkyl group (substituted orunsubstituted) as described below in more detail. The α-oxy carboxylatescan be supplied to prepare the complexes as the corresponding freecarboxylic acids or as corresponding alkali metal or ammonium salts.

In addition, the α-oxy carboxylate (L) generally has a molecular weightof 250 or less, or 150 or less, and it likely has a molecular weight ofat least 75 and up to and including 150.

It is important to note that the carboxylate groups useful in thepresent invention are not simple alkyl and aryl carboxylates that lackthe hydroxyl, alkoxy, or oxy group at the α-position.

In formula (I) shown above, b is 1 or 2, and in the embodiments where bis 2, the two α-oxy carboxylate compounds within a single complexmolecule can be the same or different compounds. For example, the twoα-oxy carboxylate compounds can be provided as two of the same moleculesrepresented by either formula (II) or (III) as described below.Alternatively, the two α-oxy carboxylate compounds can be provided bytwo different molecules represented by formula (II), two differentmolecules represented by formula (III), or one molecule represented byformula (II) and one molecule represented by formula (III).

In some embodiments of the present invention, L of formula (I) describedabove can be represented by the following formula (II):

wherein R₁, R₂, and R₃ are independently hydrogen or branched or linearalkyl groups. In most embodiments, at least one of R₁ through R₃ is abranched or linear alkyl group having from 1 to 8 carbon atoms, and anyof the hydrogen atoms in such branched or linear alkyl groups can bereplaced with a heteroatom such as a fluorine atom substituent.

In particularly useful embodiments of formula (II), R₁ is hydrogen or abranched or linear alkyl group having 1 to 3 carbon atoms (that is,substituted or unsubstituted methyl, ethyl, n-propyl, and iso-propyl),and R₂ and R₃ are independently branched or linear alkyl groups having 1to 8 carbon atoms (including iso- and tertiary alkyl groups having 3 to8 carbon atoms). In some embodiments, R₂ and R₃ are different branchedor linear alkyl groups as defined above. In addition, any of thehydrogen atoms in any of the R₁, R₂, and R₃ branched or linear alkylgroups optionally can be replaced with a fluorine atom; for example, theterminal carbon atom of a branched or linear alkyl group can have 1 to 3fluorine atoms.

Some particularly useful conjugate acids from which α-oxy carboxylates(L) of formula (II) can be selected from the group consisting of lacticacid, 2-hydroxybutyric acid, 2-hydroxy-3-methylbutyric acid,2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-isobutyric acid,2-hydroxy-2-methylbutyric acid, 2-ethyl-2-hydroxybutyric acid,2-hydroxy-2,3-dimethylbutyric acid, 2-ethyl-2-methoxybutyric acid,2-methoxy-2-methylpropanoic acid, 1-hydroxycyclopentane-1-carboxylicacid, 2,3-dihydroxy-2,3-dimethylsuccinic acid, and2,4-dihydroxy-2,4-dimethylpentanedioic acid. As noted above, mixtures ofthese materials can be used in a specific complex if desired.

In other embodiments of the present invention, L is represented informula (I) by the following formula (III):

wherein R₄ is a branched or linear alkyl group having 1 to 8 carbonatoms, including branched iso- and tertiary alkyl groups having 3 to 8carbon atoms. In addition, any of the hydrogen atoms in any of thebranched or linear alkyl groups optionally can be replaced with afluorine atom; for example, the terminal carbon atom of a R₄ branched orlinear alkyl group can have 1 to 3 fluorine atoms.

Some useful conjugate acids from which the α-oxy carboxylate (L)represented by formula (III) can be selected from the group consistingof pyruvic acid, 3-methylpyruvic acid, 3,3-dimethylpyruvic acid,3,3-dimethyl-2-oxobutanoic acid, 3,3-dimethyl-2-oxopentanoic acid, and2,3-dioxosuccinic acid.

Some helpful understanding of the electrochemical behavior of the Lgroups in formula (I) is as follows in order to understand the scope ofthis essential component of the non-hydroxylic-solvent soluble silvercomplex.

Upon oxidation, the α-oxy carboxylate identified in formula (II)undergoes decarboxylation to produce a radical K° that can undergofurther oxidation as shown in the following Equation (1):

As noted herein, the non-hydroxylic-solvent soluble silver complexaccording to this invention is characterized as having one or moremolecules of two components complexed with the silver ion: namely theα-oxy carboxylate compound and a nitrogen-containing P compound asdefined below. The chemical structural features of all of P, R₁, R₂, andR₃ determine the oxidation potential of L (E_(ox1)) whereas R₁, R₂, andR₃ determine the oxidation potential of the radical K. (E_(ox2)).

In accordance with the present invention, an α-oxy carboxylate compoundof the complex is capable of transferring two electrons to the reduciblesilver ion. The first electron comes from oxidation of the α-oxycarboxylate to generate an α-oxy carboxyl radical L. that undergoes abond cleavage reaction (decarboxylation) to give off CO₂ and to producea second radical K° that can also desirably transfer a second electronto the reducible silver ion.

Thus, L can be a fragmentable α-oxy carboxylate wherein:

(1) L has a first oxidation potential of at least 1 V and up to andincluding 2 V (or for example, at least 1.2 V and up to and including 2V);

(2) the oxidized form of L undergoes a bond cleavage reaction to providethe second radical K. and CO₂; and

(3) the second radical K. has an oxidation potential <+1V (that is,equal to or more negative than +1V), and even less than or equal to0.5V.

α-Oxy carboxylates that satisfy criteria (1) and (2) above but notcriterion (3) are capable of donating one electron to the reduciblesilver ion and are referred to herein as “fragmentable one-electrondonors”. However, α-oxy carboxylates that meet all three criteria arecapable of donating two electrons and are referred to herein as“fragmentable two-electron donors”, and such components are particularlyuseful in the practice of the invention to provide faster reduction ofthe silver ions.

Fragmentation of the oxidized form of L that is, α-oxy carboxyl radicalL., is an important feature in the silver metal-producing methodsaccording to the present invention. The kinetics of the fragmentationreaction can be measured by laser flash photolysis, a well-knowntechnique used to study properties of transient species as described forexample in “Absorption Spectroscopy of Transient Species,” W. G.Herkstroeter and I. R. Gould in Physical Methods of Chemistry Series(2nd Ed.), Volume 8, 225-319, edited by B. Rossiter and R. Baetzold,John Wiley & Sons, New York, 1993. The rate constant of fragmentation ofthe α-oxy carboxylate radical is desirably faster than about 10 persecond (that is, the lifetime of the α-oxy carboxylate radical should be10⁻⁹ seconds or less). The fragmentation rate constants can beconsiderably higher than this, namely in the 10² to 10¹³ s⁻¹ range. Inparticular, the fragmentation rate constant is desirably greater than10⁹ s⁻¹ and up to and including 10¹³ s⁻¹, or from 10¹⁰ s⁻¹ to andincluding 10¹³ s⁻¹. Fragmentation rate constants for some carboxylateradicals are known in the literature [for example see, T. MichaelBockman, Stephan M. Hubig, and Jay K. Kochi, J. Org. Chem. 1997, 62,2210-2221; James W. Hilbom and James A. Pincock, J. Am. Chem. Soc. 1991,113, 2683-2686; Daniel E. Falvey and Gary B. Schuster, J. Am. Chem. Soc.1986, 108, 1420-1422]. Fragmentation rate constants for some α-hydroxycarboxyl radicals have also been measured using laser flash photolysisand found to be very fast, that is 8×10¹¹ s⁻¹ (see, T. Michael Bockman,Stephan M. Hubig, and Jay K. Kochi, J. Org. Chem. 1997, 62, 2210-2221).Since fragmentation rates of simple alkyl and aryl carboxyl radicals areusually small (about 10⁸ to 10⁹ s⁻¹), such simple alkyl and arylcarboxylates are not useful in the practice of the present invention.

The ability of the second radical K° described above to reduce silverion indicates that the oxidation potential of K is nearly equal to ormore negative than the reduction potential of silver ion in the complex.In some useful embodiments of the present invention, the second radicalK°, resulting from the decarboxylation reaction has an oxidationpotential equal to or more negative than −0.1 V or even more negativethan −0.5 V. For example, this oxidation potential can be from −0.1 V toand including −2 V, or even from −0.5 V to and including −2 V, or morelikely from −0.1 V to and including −1.0 V. In accordance with presentinvention, an α-oxy carboxylate ion that provides a second radical K.having an oxidation potential more negative than −0.1 V is particularlyadvantageous. All oxidation potentials are vs. SCE.

The oxidation potential of many such second radicals have been measuredby transient electrochemical and pulse radiolysis techniques as reportedby Wayner, D. D., McPhee, D. J., and Griller, D. in J Am. Chem. Soc.1988, 110, 132; Rao, P. S. and Hayon, E. in J Am. Chem. Soc. 1974, 96,1287 and Rao, P. S, and Hayon, E. in J Am. Chem. Soc. 1974, 96, 1295.The reported data demonstrate that the oxidation potentials of tertiaryradicals are less positive (that is, the tertiary radicals are strongerreducing agents) than those of the corresponding secondary radicals,which in turn are more negative than those of the corresponding primaryradicals.

5- or 6-Membered N-Heteroaromatic Compounds:

A third essential component of the non-hydroxylic solvent-solublecomplexes according to the present invention is the “P” compound offormula (I), which is a 5- or 6-membered N-heteroaromatic compound. Inmany embodiments, P is a 6-membered N-heteroaromatic compound.

Such 5- or 6-membered N-heteroaromatic compounds generally have anoxidation potential of at least 1.0 V vs. SCE, or greater than 1.5 V vs.SCE, or of at least 2.0 V vs. SCE.

It is also desirable that each 5- or 6-membered N-heteroaromaticcompound useful in this invention has a pK_(a) of at least 10 and up toand including 22, or more typically of at least 10 and up to andincluding 15, as measured in acetonitrile. An experimental method formeasuring pK_(a) and the pK_(a) values of some N-heteroaromatic basesare known (for example, see Kalijurand et al. J. Org. Chem. 2005, 70,1019).

In general, the 5- or 6-membered N-heteroaromatic compound are notpolymeric in nature and has a molecular weight of 200 or less, or of 150or less, or more likely of at least 80 and up to and including 150.

By “5- or 6-membered,” it is meant that the N-heteroaromatic compoundhas either 5 or 6 atoms in the heterocyclic aromatic ring, at least oneof which atoms is a nitrogen atom. A worker of ordinary skill in the artof chemistry would be able to design any of the heteroaromatic ringsthat are possible using the laws of chemistry. In general, suchheterocyclic aromatic rings generally have at least one carbon atom andat least one nitrogen atom in the ring.

In formula (I) shown above, c is 1, 2, 3, or 4, and in the embodimentswhere c is 2, 3, or 4, the multiple 5- or 6-membered N-heteroaromaticcompound molecules within the single complex molecule can be the same ordifferent. For example, in such embodiments, one or more of the 5- or6-membered N-heteroaromatic compounds can be pyridine and other 5- or6-membered N-heteroaromatic compound(s) can be 2-methylpyridine.

Moreover, it is desirable that the 5- or 6-membered N-heteroaromaticcompound is selected from the group consisting of pyridine,2-methylpyridine, 4-methylpyridine, 2,6-dimethylpyridine,2,3-dimethylpyridine, 3,4-dimethylpyridine, 4-pyridylacetone,3-chloropyridine, 3-fluoropyridine, oxazole, 4-methyloxazole, isoxazole,3-methylisoxazole, pyrimidine, pyrazine, pyridazine, and thiazole. Otheruseful 5- or 6-membered N-heteroaromatic compounds would be readilyapparent to one skilled in the art from the foregoing description.

Representative 5- or 6-membered N-heteroaromatic compounds can bereadily obtained from various commercial chemical suppliers located invarious countries.

Method of Making Complexes

In general, the non-hydroxylic-solvent soluble silver complexesaccording to the present invention can be prepared by making a slurry ofone or more silver α-oxy carboxylates in suitable solvent mediumcomprising one or more non-hydroxylic solvents (described below) at ageneral concentration of at least 0.1 mol/I and to and including 30mol/l; and at room temperature, adding either one or more 5- or6-membered N-heteroaromatic compounds gradually to obtain a clearsolution in the resulting reaction solution. Specific details for thesesynthetic methods are provided below in the Examples.

Once prepared, the non-hydroxylic-solvent soluble silver complexes canbe stored in the form of solid (after the solvent medium is removed byevaporative methods), or left in the reaction solution under conditionsthat are optimum for long-term stability (that is, negligible premature,non-photochemical reduction of silver ion to silver metal).

Some particularly useful non-hydroxylic-solvent soluble silver complexesprepared according to the present are represented by formula (I):

(Ag⁺)_(a)(L)_(b)(P)_(c)   (I)

wherein:

a, b, and c are as defined above;

L has a molecular weight of 250 or less, and is represented by either ofthe following formula (II) or (III):

wherein R₁ is hydrogen or an alkyl group having 1 or 2 carbon atoms; R₂and R₃ are independently branched or linear alkyl groups having 1 to 8carbon atoms, wherein any of the hydrogen atoms in the R₁, R₂, and R₃branched or linear alkyl groups can optionally be replaced with afluorine atom; and R₄ is a branched or linear alkyl group having 1 to 8carbon atoms, wherein any of the hydrogen atoms optionally are replacedwith fluoride atoms;

P is a 5- or 6-membered N-heteroaromatic compound that is selected fromthe group consisting of pyridine, 2-methylpyridine, 4-methylpyridine,2,6-dimethylpyridine, 2,3-dimethylpyridine, 3,4-dimethylpyridine,4-pyridylacetone, 3-chloropyridine, 3-fluoropyridine, oxazole,4-methyloxazole, isoxazole, 3-methylisoxazole, pyrimidine, pyrazine,pyridazine, and thiazole.

Photosensitive Reducible Silver Ion-Containing Compositions

An important characteristic of the present invention is to ensure itsgeneral absorption and use in the UV to visible part of theelectromagnetic spectrum. Ideally, irradiating energy should havewavelengths in the UV to visible region (for example 350 nm to 450 nm)to allow selective excitation of the photosensitizer in the presence ofa large variety of chromophores.

The photosensitive reducible silver ion-containing compositionsaccording to the present invention contain only two essential componentsfor purposes of providing silver metal during photo-irradiation in arapid manner: (a) one or more non-hydroxylic-solvent soluble silvercomplexes according to the present invention; and (b) a solvent mediumcomprising one or more non-hydroxylic solvents as described below.However, the presence of a third component, (c) one or morephotosensitizers as described below, is very desirable in manyembodiments, also can be considered essential to assure rapidphotoreduction of silver ion at room or other low temperatures. No othercomponents are purposely added to the photosensitive reducible silverion-containing compositions according to the present invention so thatthe present invention provides simplified compositions that exhibitrapid silver metal formation for various methods and results. Theincorporation of materials other than the three components (a) through(c) is likely to impede the generation of metallic silver.

The (a), (b), and (c) components can be put together in general bymixing them under “safe light” (yellow light) conditions if desired.This mixing can occur in suitable solvent medium (as described below)comprising one of more of the (b) solvents. The resulting photosensitivereducible silver ion-containing composition can be provided in liquidform having a viscosity of at least 1 centipoise and up to and including1,000 centipoises at 25° C.

The one or more non-hydroxylic-solvent soluble silver complexes can bepresent in an amount of at least 5 weight % and up to and including 90weight %, based on the total weight of the photosensitive reduciblesilver ion-containing composition.

Thus, in some embodiments, the photosensitive reducible silverion-containing composition can comprise two or more differentnon-hydroxylic-solvent soluble silver complexes. Such embodiments canalso include two or more different photosensitizers as described below.

The photosensitive reducible silver ion-containing composition of claim1 has exceptive long term stability as demonstrated by a silverstability test such that when the photosensitive reducible silverion-containing composition is held at ambient temperature (20° C. to 25°C.) and under yellow safelight for 24 hours, less than 0.1 mol % of itsoriginal silver ion content is reduced to silver metal.

Solvent Medium:

The essential non-hydroxylic-solvent soluble silver complex (andphotosensitizer if present) are generally solubilized in a suitablesolvent medium that is predominantly non-hydroxylic organic solventsthat include but are not limited to, acetonitrile, benzonitrile,acetone, methyl ethyl ketone, butyronitrile, propylene carbonate,propionitrile, isovaleronitrile, valeronitrile, and a mixture of two ormore thereof. It is also desirable that the non-hydroxylic solvents donot participate in any redox reaction. That is, such non-hydroxylicsolvents should not be capable under general preparation, storage, anduse conditions to reduce silver ion by transferring electrons or tooxidize an α-oxy carboxylate by accepting electrons. Such reactions bynon-hydroxylic solvents would negatively impact the thermal stability ofphotosensitive compositions according to the present invention.

Water is not purposely added to the solvent medium, and if water ispresent, it should be present at no more than 5 weight % based on thetotal weight of the solvent medium (not including thenon-hydroxylic-solvent soluble silver complex and photosensitizer).

Photosensitizers:

The photosensitizers useful in the present invention initiate theelectrochemical transformation of the non-hydroxylic-solvent solublesilver complexes. The photosensitizer must be capable of either reducingthe silver ions or oxidizing the α-oxy carboxylates after thephotosensitizer has absorbed light (that is, photoinduced electrontransfer) at an electromagnetic radiation having a wavelength of atleast 150 nm and up to and including 700 nm. Thus, the photosensitivecompositions according to this invention are generally sensitive to UVor visible electromagnetic radiation, or both, sufficient to convert thereducible silver ions in the non-hydroxylic reducible silver-containingcomplexes to silver metal. Such complexes containing reducible silverions are inherently photosensitive to some degree but the presence ofone or more photosensitizers as described herein enhancesphotosensitivity for much more effective and rapid reduction ofreducible silver ions to silver metal. It is particularly useful to usephotosensitizers that enhance sensitivity to electromagnetic radiationhaving a wavelength of at least 190 nm and up to and including 450 nm,or even of at least 250 nm and up to and including 450 nm.

The amount of photosensitizer used in the photosensitive reduciblesilver ion-containing composition depends largely on its optical densityand extinction coefficient at the wavelength(s) of radiation used tosensitize silver ion reduction. A photosensitizer with a low extinctioncoefficient can be utilized at relatively high levels and vice versa.Solubility of the photosensitizer can also be a factor in the amountthat is used. In general, one or more photosensitizers described hereincan be present in the photosensitive reducible silver ion-containingcompositions in an amount of least 0.5 weight % and up to and including4 weight %, or at least 1 weight % and up to and including 3 weight %,all amounts being based on the total weight of the one or morenon-hydroxylic-solvent soluble silver complexes in the photosensitivereducible silver ion-containing composition. Thus, in some embodiments,two or more different photosensitizers can be used together.

There are two distinct classes of photosensitizers that can be used inthe invention.

In some embodiments, the photosensitizers are electron-acceptingphotosensitizers that upon absorption of the incident radiation arecapable of oxidizing the α-oxy carboxylate to initiate the reaction forsilver ion reduction.

To determine whether a photosensitizer is capable of oxidizing thecarboxylate ion in the non-hydroxylic solvent-soluble complex to aradical after the photosensitizer has absorbed suitable radiation,reaction energetics can be used. There are four controlling parametersin these reaction energetics: (1) the excitation energy of anelectron-accepting photosensitizer (E_(S)*); (2) the reduction potential(E_(S) ^(red)) of the electron-accepting photosensitizer (S); (3) thereduction potential (E_(Ag+) ^(red)) of the silver ion in thenon-hydroxylic-solvent soluble complex; and (4) the oxidation potential(E_(C) ^(ox)) of the α-oxy carboxylate in the complex (C) that is anelectron donor. For these reactions to be energetically feasible, theenergy of the excited state should be higher or only slightly lower thanthe energy stored in the primary product of initial electron transfer,the radical ion pair (E_(IP)), C.S⁺..

The excitation energy of the electron-accepting photosensitizer (S) canbe conveniently determined from the midpoint of the normalizedabsorption and emission spectrum of the compound, if the reactionproceeds from the singlet excited state. However, if the reactionproceeds via the triplet state, then the triplet energy of theelectron-accepting photosensitizer can be used as the excitation energy.

The energy of the radical ion pair, E_(IP), is given by Equation (2)below, where A is an energy increment that depends on the mediumpolarity and ranges from nearly zero in highly polar media to about 0.3eV in the least polar media. The electrochemical measurements arecarried out in polar solvents such as acetonitrile or methylenechloride.

E _(IP) =E _(C) ^(ox) −E _(S) ^(red)+Δ  Equation (2).

Thin photosensitive films according to the present invention areexpected to be lower in dielectric constant, and as a result would notstrongly solvate the radical ion pair. Thus, the energy increment A inEquation (1) noted above is expected to be near the maximum value, thatis, in the range of 0.2 eV to 0.3 eV.

Accordingly, electron-accepting photosensitizers with an excitationenergy equal to or larger than the difference between the oxidationpotential of the α-oxy carboxylate in the complex (C) and the reductionpotential of the electron-accepting photosensitizer (E_(C) ^(ox)−E_(S)^(red)), will satisfy the energetic requirements of photoinitiating thereaction according to the following Equation (3):

E _(S) *≧E _(C) ^(ox) −E _(S) ^(red)+Δ  Equation (3).

Since the Δ value in the current system is expected to be in the rangeof from 0.2 eV to 0.3 eV, it is more convenient to express the energeticrequirements of the electron-accepting photosensitizer relative to thedonor in terms of a rearranged form in the following Equation (4):

E _(S) *+E _(S) ^(red) ≧E _(C) ^(ox)  Equation (4).

According to Equation (4), for the reaction to be energeticallyfeasible, the algebraic sum of the excitation energy of theelectron-accepting photosensitizer and its reduction potential should beapproximately equal to or greater than the oxidation potential of theα-oxy carboxylate ion in the non-hydroxylic-solvent soluble silvercomplex (C).

In general, many different compounds can be used as electron acceptingphotosensitizers according to the present invention, provided that theenergetic requirements discussed above are satisfied. Representativeelectron-accepting photosensitizers include but are not limited to,cyano-substituted aromatic carbocyclic compounds (such as1-cyanonaphthalene, 1,4-dicyanonaphthalene, 9,10-dicyanoanthracene,2,9,10-tricyanoanthracene, and 2,6,9,10-tetracyanoanthracene); aromaticanhydrides and imides (such as 1,8-naphthylene dicarboxylic,1,4,6,8-naphthalene tetracarboxylic, 3,4-perylene dicarboxylic, and3,4,9,10-perylene tetracarboxylic anhydride or imide); and condensedpyridinium salts (such as quinolinium, isoquinolinium, phenanthridiniumsalts; and pyrylium salts). Representative electron-acceptingphotosensitizers that involve the triplet excited state include but arenot limited to, carbonyl compounds (such as quinones such as benzo-,naphtho-, and anthro-quinones having electron withdrawing substituentssuch as chloro or cyano groups). Ketocoumarins having strong electronwithdrawing moieties such as a pyridinium group, are also useful aselectron-accepting photosensitizers.

For the specific example of an α-oxy carboxylate, which has a peakoxidation potential of −1.4 V vs. SCE, numerous electron-acceptingphotosensitizers that meet the requirement of the above Equation (3),can be used. For example, electron-accepting photosensitizers useful inthe present invention include but are not limited to PS-1 through PS-8in the following TABLE I.

TABLE I E_(s)* E_(s) ^(red) PS-1

2.92 −0.91 PS-2

3.82 −1.88 PS-3

3.53 −0.7 PS-4

2.85 −0.4 PS-5

2.9 −0.4 PS-6

2.13 0.0 PS-7

2.53 −1.1 PS-8

3.1 −0.29

In other embodiments of the present invention, upon absorption of notedelectromagnetic radiation, the electron-donating photosensitizer (S)transfers an electron to the reducible silver ion in thenon-hydroxylic-solvent soluble silver complex to form a photosensitizerradical cation (S⁺.) as shown in Equation (5) below, which in turnoxidizes the α-oxy carboxylate (L) to produce radical K. (see Equation(6) below). For photosensitizer radical cation (S⁺.) to be able tooxidize the α-oxy carboxylate (L), the oxidation potential of theelectron donating photosensitizer (S) has to be greater than that of theα-oxy carboxylate.

(Ag⁺)_(a)(L)_(b)(P)_(c)+S*→Ag⁰(L)_(b)P_(c)+S⁺⁻  (Eq. 5)

Ag⁰(L)_(b)(P)_(c)+S⁺⁻→Ag⁰(K*)_(b)(P)_(c)+S  (Eq. 6)

To determine whether an electron-donating photosensitizer is capable ofreducing the reducible silver ion after it has absorbed electromagneticradiation, reaction energetics described above in Equations (2) and (3)can be used. Thus, for the reaction to be energetically feasible, thedifference of electron-donating photosensitizer excitation energy andits oxidation potential should be approximately equal to or larger thanthe reduction potential of the silver ion in the complex (E_(Ag+)^(red)) [see Equation (7) below].

E _(S) *−E _(S) ^(ox) ≧−E _(Ag+) ^(red)  Equation (7)

For the specific example of the reduction of reducible silver ion thathas a peak reduction potential of −0.1 V vs. SCE, numerouselectron-donating photosensitizers that meet the requirement of Equation(7) can be used.

The excitation energy of the electron-donating photosensitizer (S) isconveniently determined from the midpoint of its normalized absorptionand emission spectrum if the reaction proceeds from the singlet excitedstate. However, if the reaction proceeds via the triplet state, then thetriplet energy of the electron-donating photosensitizer should be usedas the excitation energy.

In most embodiments, the electron-donating photosensitizer can beselected so that its oxidation potential is greater than that of α-oxycarboxylate. Some representative examples of such electron-donatingphotosensitizers, namely those having the difference of excitationenergy and oxidation potential that is equal to or exceeds −0.1 V vs.SCE, include but not limited to, compounds PS-9 to PS-18 as shown in thefollowing TABLE II.

TABLE II E_(s)* E_(s) ^(ox) PS-9 

3.2 0.98 PS-10

3.67 1.16 PS-11

2.43 1.77 PS-12

2.52 1.77 PS-13

NA NA PS-14

2.42 1.8 PS-15

2.42 1.8 PS-16

3.3 1.3 PS-17

3.3 1.3 PS-18

3.4 1.5 NA means “not available”.

Oxidation potentials for many electron-accepting and electron-donatingphotosensitizers are known and can be found, for example, in theEncyclopedia of Electrochemistry of the Elements, Organic Section,Volumes XI-XV, A. Bard and H. Lund (Editors) Marcel Dekkar Inc., NY(1984). If unavailable in the literature, oxidation potentials of usefulelectron-accepting and electron-donating photosensitizers can bemeasured by cyclic voltammetry using known equipment and procedures.

Thus, in some embodiments of the present invention, the photosensitizeris present, and when the photosensitizer is an electron-donatingphotosensitizer, it is defined by Equation (7) noted above, and when thephotosensitizer is an electron-accepting photosensitizer, it is definedby Equation (4) noted above:

wherein:

E_(S) ^(ox) is the oxidation potential of the electron-donatingphotosensitizer;

E_(S)* is the excitation energy of the electron-acceptingphotosensitizer;

E_(S) ^(red) is the reduction potential of the electron-acceptingphotosensitizer;

E_(Ag+) ^(red) is the reduction potential of the silver ion in thenon-hydroxylic-solvent soluble silver complex; and

E_(C) ^(ox) is the oxidation potential of the α-oxy carboxylate.

Precursor Articles

The non-hydroxylic-solvent soluble silver complexes and photosensitivereducible silver ion-containing compositions according to the presentinvention can be used to provide “precursor” articles that can then beused in various operations to provide electrically-conductive silvermetal-containing thin film layers or electrically-conductive silvermetal-containing thin film patterns for various uses in “productarticles” as described below.

The term “precursor article” refers to an article (or element) designedto have a substrate having thereon a photosensitive thin film orphotosensitive thin film pattern comprising a photosensitive reduciblesilver ion-containing composition as noted above as well as one or morephotosensitizers and thus, are article in which silver reduction has notoccurred to any appreciable extent.

The term “product article” then refers to an article (or element) inwhich silver ion reduction has occurred to at least some extent andhopefully to a significant extent during chosen operations as describedbelow. Such product articles comprise a substrate having thereon asilver metal-containing thin film or silver metal-containing thin filmpattern.

Both precursor articles and product articles have at least one featurein common, that is a suitable substrate that generally has two planarsurfaces: a first supporting side (or surface) and a second opposingsupporting side (or surface). Such substrates can have any suitable formsuch as sheets of any desirable size and shape, elongated fibers orwoven fibers (such as in textiles) or other porous materials, polymericbeads of regular or irregular surface configuration (such as a curved ornon-planar surface), and especially continuous webs of various materialsthat can be supplied, used, or stored as rolls.

More specifically, a uniform photosensitive thin film or one or morephotosensitive thin film patterns are provided in a suitable manner onone or more supporting (planar) sides of a suitable substrate to providea precursor article according to the present invention. Typically,photosensitive thin films or photosensitive thin film patterns areinitially “wet” during and immediately after application to thesubstrate but the solvent medium can be removed as described below toprovide the desired photosensitive thin films or photosensitive thinfilm pattern(s).

The photosensitive reducible silver ion-containing compositionsaccording to this invention can be applied in a uniform or pattern-wisemanner to any suitable substrate using any means for application, suchas dip coating, roll coating, hopper coating, screen printing, spraycoating, spin coating, inkjet printing, photolithographic imprinting,flexographic printing using printing elements including flexographicprinting members (such as flexographic printing plates and flexographicprinting sleeves), lithographic printing using lithographic printingplates, and gravure or intaglio printing using appropriate printingmembers. Inkjet printing and flexographic printing are particularlyuseful for providing photosensitive thin film patterns on one or bothsupporting sides of the substrate.

Suitable substrates (also known as “receiver elements”) can be composedof any suitable material as long as it does not inhibit the purpose ofthe present invention to form silver metal within a uniform thin film orthin film pattern. For example, substrates can be formed from materialsincluding but are not limited to, polymeric films, metals, glasses(untreated or treated for example with tetrafluorocarbon plasma,hydrophobic fluorine, or a siloxane water-repellant material), siliconor ceramic materials such as ceramic wafers, fabrics, papers, andcombinations thereof (such as laminates of various films, or laminatesof papers and films) provided that a uniform thin film or thin filmpattern can be formed thereon in a suitable manner and followed byirradiation on at least one supporting side thereof. The substrate canbe transparent or opaque, and rigid or flexible.

The substrate can include one or more auxiliary polymeric ornon-polymeric layers or one or more patterns of other materials beforethe photosensitive reducible silver ion-containing composition isapplied according to the present invention.

Suitable substrate materials for forming precursor and product articlesaccording to the present invention include but are not limited to,metallic films or foils, metallic films on polymer, glass, or ceramicmaterials, metallic films on electrically conductive film supports,semi-conducting organic or inorganic films, organic or inorganicdielectric films, or laminates of two or more layers of such materials.For example, useful substrates can include polymeric films such aspoly(ethylene terephthalate) films, poly(ethylene naphthalate) films,polyimide films, polycarbonate films, polyacrylate films, polystyrenefilms, polyolefin films, and polyamide films, silicon and other ceramicmaterials, metal foils such as aluminum foils, cellulosic papers orresin-coated or glass-coated papers, glass or glass-containingcomposites, metals such as aluminum, tin, and copper, and metalizedfilms. Porous fabrics, glasses, and polymeric webs can also be used.

Particularly useful substrates are polyesters films such as films ofpoly(ethylene terephthalate), polycarbonate, or poly(vinylidenechloride) films with or without surface-treatments or coatings as notedbelow, including continuous flexible webs of such polymers.

Either or both supporting sides (or surfaces) of the substrate can betreated for example with a primer layer or electrical or mechanicaltreatments (such as graining) to render that surface “receptive” toimprove adhesion of the photosensitive reducible silver ion-containingcomposition and resulting photocured silver-containing thin film orphotocured silver-containing thin film pattern. An adhesive layer can bedisposed on the substrate and this adhesive layer can have variousproperties in response to stimuli (for example, it can be thermallyactivated, solvent activated, or chemically activated) and that servesto provide a receptive layer. Useful adhesive materials of this type aredescribed for example in [0057] of U.S. Patent Application 2008/0233280(Blanchet et al.).

In some embodiments, the substrate comprises a separate receptive layeras a receptive surface disposed on the supporting side of the substrate,which receptive layer and substrate can be composed of a material suchas a suitable polymeric material that is highly receptive of thephotosensitive reducible silver ion-containing composition. Such areceptive layer can have any suitable dry thickness of at least 0.05 μmwhen measured at 25° C.

The two (planar) supporting sides of the substrate, especially polymericsubstrates, can be treated by exposure to corona discharge, mechanicalabrasion, flame treatments, or oxygen plasmas, or by coating withvarious polymeric films, such as poly(vinylidene chloride) or anaromatic polysiloxane as described for example in U.S. Pat. No.5,492,730 (Balaba et al.) and U.S. Pat. No. 5,527,562 (Balaba et al.)and U.S. Patent Application Publication 2009/0076217 (Gommans et al.).

Useful substrates can have a desired dry thickness depending upon theeventual use of the precursor article formed therefrom, for example itsincorporation into various products articles or optical or displaydevices. For example, the substrate dry thickness (including alltreatments and auxiliary layers) can be at least 0.001 mm and up to andincluding 10 mm, and especially for polymeric films, the substrate drythickness can be at least 0.008 mm and up to and including 0.2 mm.

The substrate used to prepare the precursor and product articlesdescribed herein can be provided in various forms, such as for example,individual sheets in any size or shape, and continuous webs such ascontinuous webs of transparent substrates including transparentpolyester substrates that are suitable for roll-to-roll operations. Suchcontinuous webs can be divided or formed into individual first, second,and additional portions on first and second opposing supporting sidesthat can be used to form the same or different photosensitive thin filmpatterns in different portions of a supporting side (such as the firstsupporting sides) as well as same or different photoreducedsilver-containing thin film patterns from the same or differentphotosensitive reducible silver ion-containing compositions.

In general, in the precursor article according to the present invention,the one or more non-hydroxylic-solvent soluble silver complexes can bepresent in the photosensitive thin film or the one or morephotosensitive thin film patterns in a total amount of at least 95weight % and up to and including 99 weight % based on the total dryweight of the photosensitive thin film or the one or more photosensitivethin film patterns. Moreover, one or more photosensitizers can bepresent in a total amount of at least 0.1 weight % and up to andincluding 4 weight %, or at least 1 weight % and up to and including 3weight %, all photosensitizer amounts being based on the total amount ofthe total non-hydroxylic-solvent soluble silver complexes.

In some embodiments, a precursor article can further comprise one ormore photosensitive thin film patterns on the second opposing supportingside of the substrate, each of the one or more photosensitive thin filmpatterns disposed on the second opposing supporting side, comprising:

a) one or more non-hydroxylic-solvent soluble silver complexes asdescribed above; and

b) one or more photosensitizers as described above.

Product Articles

The product articles provided by the methods according to the presentinvention described below generally have the same structure andcomponents as the precursor articles except that most or all of thereducible silver ions have been reduced to electrically-conductivesilver metal in the corresponding electrically-conductive thin films orelectrically-conductive thin film patterns. In some embodiments, theproduct articles can be provided in any suitable form such as individualsheets of any suitable size and shape, films or webs whose ends areattached to each other, wound rolls of continuous material with orwithout a core material, spindle, or mandrel.

In other embodiments, where inventive complexes, photosensitivecompositions, and methods can be used to generateelectrically-conductive metallic silver patterns and electrodes withinvarious devices, including but not limited to, membrane touch switch(MTS), battery testers, biomedical, electroluminescent lamps, radiofrequency identification (RFID) antenna, flat panel displays such asplasma display panel (PDP) and organic light emitting diode (OLED)display, printed transistors and circuits, thin film photovoltaics, andother devices that would be readily apparent to one skilled in the art.In other words, such “product” articles according to this invention aredevice themselves rather than articles that are incorporated into adevice. Alternatively, the product articles are devices themselves thatalso have another product article incorporated therein.

Electrically-conductive thin film patterns can be created according tothe present invention using photolithography to create high-fidelityfeatures. Both positive and negative patterning processes may be used tocreate such patterns.

Such product articles comprise a substrate having a first supportingside and a second opposing supporting side. On at least the firstsupporting side, are:

an electrically-conductive silver metal-containing thin film or one ormore electrically-conductive silver metal-containing thin film patterns,comprising:

silver metal;

an α-oxy carboxylate (residual amounts of the L component from formula(1)) as described above;

a 5- or 6-membered N-heteroaromatic compound (residual amounts of the Pcomponent from formula (1)); and

one or more photosensitizers as described above that can either reducereducible silver ion or oxidize the α-oxy carboxylate.

Depending upon how the precursor article is designed, the productarticle can comprise two or more electrically-conductive silvermetal-containing thin film patterns in different portions on the firstsupporting side of the substrate.

In addition, a product article can further comprise one or moreelectrically-conductive silver metal-containing thin film patterns indifferent portions on the second opposing supporting side of thesubstrate,

each of these one or more electrically-conductive silvermetal-containing thin film patterns comprising:

silver metal;

an α-oxy carboxylate (that is, residual amounts of the L component offormula (1) as described above);

a 5- or 6-membered N-heteroaromatic compound (that is, residual amountsof the P component of formula (1) described above); and

one or more photosensitizers as described above that can either reducereducible silver ion or oxidize the α-oxy carboxylate.

For example, in such embodiments, the product articles can comprise:

silver metal;

residual α-oxy carboxylate having a molecular weight of 150 or less, andthat is represented by either the following formula (II) or (III):

wherein R₁ is hydrogen or a branched or linear alkyl group having 1 to 3carbon atoms, R₂ and R₃ are independently branched or linear alkylgroups having 1 to 8 carbon atoms, wherein any of the hydrogen atoms inthe R₁, R₂, and R₃ branched or linear alkyl groups optionally can bereplaced with a fluorine atom, and R₄ is a branched or linear alkylgroup having 1 to 8 carbon atoms wherein any of the hydrogen atomsoptionally can be replaced with a fluorine atom; and

residual 5- or 6-membered N-heteroaromatic compound that is selectedfrom the group consisting of pyridine, 2-methylpyridine,2,6-dimethylpyridine, 3-chloropyridine, 3-fluoropyridine, oxazole,4-methyloxazole, isoxazole, 3-methylisoxazole, pyrimidine, pyrazine,pyridazine, and thiazole.

Method for Providing Silver Metal

The precursor articles are prepared and used according to the presentinvention by firstly providing a suitable photosensitive thin film on asubstrate as described above. This can be accomplished in a number ofways.

In some embodiments, a photosensitive reducible silver ion-containingcomposition according to the present invention can be disposed in auniform manner onto one or both supporting sides of the substrate (withor without adhesion treatments), such as a polymeric film (for example,as a continuous polyester web), glass, paper, cardboard, or ceramicmaterial A variety of films, including for example polymer filmscomposed of polyethylene, polypropylene, biaxially orientedpolypropylene, polyethylene terephthalate, polybutylene terephthalateand polyamide, can be utilized as suitable substrates. The choice ofsubstrate structure is not, however, limited to films but includespolymers or copolymers or polymer blends formed into bags, shrink wrap,plates, cartons, boxes, bottles, crates, and other containers.Similarly, the range of suitable substrate compositions is not limitedto polymers and copolymers, but can include papers such as pre-coatedpapers, cardboard such as pre-coated cardboard, and other commonpackaging materials. Such composition application can be carried out forexample, uniform inkjet printing or using a blade coating, gap coating,slot die coating, X-slide hopper coating, or knife on roll operation.

After application of the photosensitive reducible silver ion-containingcomposition in this manner, if desired, at least 50 weight % and up toand including 100 weight % of the original solvent medium (and anywater) can be removed in any suitable manner. For example, ambientdrying can be carried out in an open environment, of the resultingprecursor article can be subject to an “active” drying operation andapparatus that do not adversely affect the non-hydroxylic-solventsoluble silver complex (and photosensitizer if present) in the precursorarticle, or prematurely cause reduction of the silver ions. Usefuldrying conditions can be as low as room temperature for as little as 5seconds and up to and including several hours depending upon themanufacturing process. In many processes, such as roll-to-roll processesin manufacturing operations, drying conditions can be employed at anysuitable temperature, for example greater than 50° C. to remove at least90 weight % (and up to 100 weight %) of the original solvent medium (andany water) within at least 10 seconds or within 5 seconds or within 1second.

The one or more non-hydroxylic-solvent soluble silver complexes can bepresent in the photosensitive thin film or photosensitive thin filmpattern in an amount of at least 96 weight % and up to and including99.5 weight % based on the total weight of the photosensitive thin filmor photosensitive thin film pattern; and the photosensitizer is presentin an amount of at least 0.5 weight % and up to and including 4 weight%, based on the total weight of the one or more non-hydroxylic-solventsoluble silver complexes.

The resulting photosensitive thin films generally have a dry averagethickness of at least 100 nm and up to and including 1,500 nm, or morelikely at least 500 nm and up to and including 1000 nm (“average”determined by two or more measurements in different locations). The drythickness can vary to some degree throughout the photosensitive thinfilm. The term “uniform” in this context does not necessary mean thatthe dry thickness must always be the same, but that the entire surfaceof the supporting side of the substrate is completely covered.

Alternative to depositing the photosensitive reducible silverion-containing composition in a uniform manner, it can be applied to thesubstrate (one or both supporting sides) in a patternwise fashion usingtechniques described below such as flexographic printing or inkjetprinting to provide one or more photosensitive thin film patterns.

Any applied photosensitive thin film pattern can comprise a grid oflines (or other shapes including circles or an irregular network), eachhaving a dry average thickness (or width) of at least 1000 nm and up toand including 10 mm, or typically of at least 5 μm and up to andincluding 1 mm, and the optimal dry thickness (or width) can be tailoredfor an intended use.

In some embodiments, the same or different photosensitive reduciblesilver ion-containing composition can be applied in a suitable manner indifferent portions on both the first supporting side and the secondopposing supporting side of the substrate to form “duplex” or dual-sidedprecursor articles, and each applied photosensitive reducible silverion-containing composition can be in the form of the same or differentphotosensitive thin film pattern.

In many embodiments, a photosensitive reducible silver ion-containingcomposition is applied on one or both supporting sides of the substrate(for example as a roll-to-roll web) using a relief element such aselastomeric relief elements derived from flexographic printing plateprecursors, many of which are known in the art and some are commerciallyavailable, for example as the CYREL® Flexographic Photopolymer Platesfrom DuPont and the Flexcel SR and NX Flexographic plates from EastmanKodak Company.

Particularly useful elastomeric relief elements are derived fromflexographic printing plate precursors and flexographic printing sleeveprecursors, each of which can be appropriately imaged (and processed ifneeded) to provide the relief elements for “printing” suitablephotosensitive thin film patterns as described for example, in U.S. Pat.No. 7,799,504 (Zwadlo et al.) and U.S. Pat. No. 8,142,987 (Ali et al.)and U.S. Patent Application Publication 2012/0237871 (Zwadlo), thedisclosures of all of which are incorporated herein by reference fordetails of such flexographic printing member precursors. Suchelastomeric photopolymerizable layers can be imaged through a suitablemask image to provide an elastomeric relief element (for example,flexographic printing plate or flexographic printing sleeve). The relieflayer can be different if different patterns of photosensitive reduciblesilver ion-containing compositions are applied to opposing supportingsides of the substrate.

In other embodiments, the elastomeric relief element is provided from adirect (or ablation) laser-engraveable elastomer relief elementprecursor, with or without integral masks, as described for example inU.S. Pat. No. 5,719,009 (Fan), U.S. Pat. No. 5,798,202 (Cushner et al.),U.S. Pat. No. 5,804,353 (Cushner et al.), U.S. Pat. No. 6,090,529(Gelbart), U.S. Pat. No. 6,159,659 (Gelbart), U.S. Pat. No. 6,511,784(Hiller et al.), U.S. Pat. No. 7,811,744 (Figov), U.S. Pat. No.7,947,426 (Figov et al.), U.S. Pat. No. 8,114,572 (Landry-Coltrain etal.), U.S. Pat. No. 8,153,347 (Veres et al.), U.S. Pat. No. 8,187,793(Regan et al.), and U.S. Patent Application Publications 2002/0136969(Hiller et al.), 2003/0129530 (Leinenback et al.), 2003/0136285 (Telseret al.), 2003/0180636 (Kanga et al.), and 2012/0240802 (Landry-Coltrainet al.), the disclosures of all of which are incorporated herein fordetails of such laser-engraveable precursors.

When the noted elastomeric relief elements are used in the presentinvention, the photosensitive reducible silver ion-containingcomposition can be applied in a suitable manner to the uppermost reliefsurface (raised surface) in the elastomeric relief element. Applicationto a substrate can be accomplished in a suitable procedure and it isdesirable that as little as possible is coated onto the sides (slopes)or recesses of the relief depressions. Anilox roller systems or otherroller application systems, especially low volume Anilox rollers, below2.5 billion cubic micrometers per square inch (6.35 billion cubicmicrometers per square centimeter) and associated skive knives can beused.

In such embodiments, the photosensitive reducible silver ion-containingcomposition can have a viscosity during this application of at least 1cps (centipoise) and up to and including 5000 cps, or at least 1 cps toand up to and including 1500 cps. The photosensitive reducible silverion-containing composition can be fed from an Anilox or other rollerinking system in a measured amount for each printed precursor article.In one embodiment, a first roller can be used to transfer thephotosensitive reducible silver ion-containing composition from an “ink”pan or a metering system to a meter roller or Anilox roller. Suchcomposition is generally metered to a uniform thickness when it istransferred from the Anilox roller to a printing plate cylinder. Whenthe substrate is moved through the roll-to-roll handling system from theprinting plate cylinder to an impression cylinder, the impressioncylinder applies pressure to the printing plate cylinder that transfersan image from an elastomeric relief element to the substrate in forminga precursor article.

Once the photosensitive thin films or photosensitive thin film patternsare provided, such precursor articles can be then appropriately exposed(for example using radiation having a wavelength of at least 150 nm andup to and including 700 nm) to photochemically convert the reduciblesilver ions to silver metal, for example in the presence of oxygen, toprovide product articles comprising silver metal-containing thin filmsor one or more silver metal-containing thin film patterns. This exposingoperation can be carried out at room temperature or more likely undereither ambient or controlled conditions at a temperature of at least 45°C. It would be apparent that such temperature conditions can vary withthe specific exposing devices that are used.

For example, irradiation can be carried out using a suitable source suchas a fluorescent lamp or LED to provide a silver metal-containing thinfilm or silver metal-containing thin film pattern. For example, silverion reduction can be achieved by the use of UV or visible irradiationhaving a wavelength of at least 150 nm and up to and including 700 nmand at intensity of at least 1,000 microwatts/cm² and up to andincluding 80,000 microwatts/cm². The irradiation system used to generatesuch radiation can consist of one or more ultraviolet lamps for examplein the form of 1 to 50 discharge lamps, for example, xenon, metallichalide, metallic arc (such as a low, medium or high pressure mercuryvapor discharge lamps having the desired operating pressure from a fewmillimeters to about 10 atmospheres). The lamps can include envelopescapable of transmitting light of a wavelength of at least 150 nm and upto and including 700 nm or typically at least 240 nm and up to andincluding 450 nm. The lamp envelope can consist of quartz, such asSpectrocil or Pyrex. Typical lamps that can be employed for providingultraviolet radiation are, for example, medium pressure mercury arcs,such as the GE H3T7 arc, a Hanovia 450 W are lamp, and Fusion F300S,F600S, and F300SQ microwave-powered electrodeless lamps. Silver ionphotochemical reduction can be carried out using a combination ofvarious lamps, some of or all of which can operate in an inertatmosphere. When using UV lamps, the irradiation flux impinging upon thesubstrate (or applied layer or pattern) can be at least 0.01 watts/inch²(0.0197 watts/cm²) to effect sufficient rapid silver ion photoreductionwithin 1 to 20 seconds in a continuous manner, for example in aroll-to-roll operation. In some embodiments, a pulsed light source canbe used to cause the photochemical reaction. The duration and rate ofpulse can be varied to achieve the desired light dosage within thedesired irradiation time.

An LED irradiation device to be used in the photochemical reduction canhave an emission peak wavelength of 350 nm or more. The LED device caninclude two or more types of elements having different emission peakwavelengths greater than or equal to 350 nm. A commercial example of anLED device that has an emission peak wavelength of 350 nm or more andhas an ultraviolet light-emitting diode (UV-LED) is NCCU-033 that isavailable from Nichia Corporation.

Each precursor article can be irradiated individually as a singleelement, or in alternative embodiments, as a web (for example, aroll-to-roll continuous web) containing multiple precursor articles inmultiple portions of the continuous web that is passed through exposurestations, or the exposure device is passed over the continuous web. Thesame or different photosensitive reducible silver ion-containingcompositions can be applied (for example, printed) on both supportingsides of the substrate whether it is in the form of a single element orcontinuous web. In many embodiments, different photosensitive thin filmpatterns can be formed on opposing supporting sides of the substrate (orcontinuous web).

The result of such irradiation of a precursor article is a productarticle as described above comprising the substrate (for example,individual sheets or a continuous web) and having thereon either anelectrically-conductive silver metal-containing thin film or one or moreelectrically-conductive silver metal-containing thin film patterns onone or both supporting sides of the substrate.

In general, the electrically-conductive silver metal-containing thinfilm or electrically-conductive silver-containing thin film patterns hasa resistivity of less than 10⁶ ohms/o as measured using a 4-point probedevice. In particular embodiments, each electrically-conductivesilver-containing thin film or electrically-conductive silver-containingthin film pattern has a resistivity of less than 1000 ohms/o, or aresistivity of less than 500 ohm/o, or even less than 100 ohms/D.

After irradiation, the product articles can be contacted (washed) withwater for up to 5 minutes at a temperature of at least 20° C. and up toand including 90° C. Such water contacting can be used to removeimpurities as well as to enhance electrical conductivity of theelectrically-conductive silver metal-containing thin film or one or moreelectrically-conductive silver metal-containing thin film patterns.Residual water can be removed after this step using any suitable dryingoperation, for example as described above for other drying operations.

In some embodiments, a method according to the present invention forproviding two or more electrically-conductive patterns on a continuoussubstrate having a first supporting side and a second opposingsupporting side, comprises:

providing a continuous substrate,

providing two or more photosensitive thin film patterns on two or morerespective portions on the first supporting side of the continuoussubstrate, each of the two or more photosensitive thin film patternscomprising:

a) a non-hydroxylic-solvent soluble silver complex comprising: areducible silver ion complexed with an α-oxy carboxylate and a 5- to6-membered N-heteroaromatic compound,

the non-hydroxylic-solvent soluble silver complex being represented bythe following formula (I):

(Ag⁺)_(a)(L)_(b)(P)_(c)   (I)

wherein L represents the α-oxy carboxylate; P represents the 5- or6-membered N-heteroaromatic compound; a is 1 or 2; b is 1 or 2; and c is1, 2, 3, or 4,

provided that when a is 1, b is 1, and when a is 2, b is 2; and

b) a photosensitizer that can either reduce the reducible silver ion oroxidize the α-oxy carboxylate;

photochemically converting reducible silver ions in each of the two ormore photosensitive thin film patterns on the first supporting side ofthe continuous substrate to provide correspondingly two or moreelectrically-conductive silver metal-containing patterns;

contacting each of the two or more electrically-conductive silvermetal-containing patterns with water or an aqueous or non-aqueous saltsolution (as described below);

optionally, contacting each of the two or more electrically-conductivesilver metal-containing patterns with an aqueous or non-aqueous non-saltsolution (as described below); and

optionally, drying each of the two or more electrically-conductivesilver metal-containing patterns on the supporting side of thecontinuous substrate. Such drying can be carried out using any suitabledrying conditions and equipment, for example as described above forother drying operations.

Such a method can further comprise:

providing two or more opposing photosensitive thin film patterns on twoor more respective portions on the second opposing supporting side ofthe continuous substrate, each of the two or more opposingphotosensitive thin film patterns comprising:

a) the non-hydroxylic-solvent soluble silver complex; and

b) the photosensitizer;

photochemically converting reducible silver ions in each of the two ormore opposing photosensitive thin film patterns to provide two or moreopposing electrically-conductive silver metal-containing patterns on thesecond opposing supporting side of the continuous substrate;

contacting each of the two or more opposing electrically-conductivesilver metal-containing patterns with water or an aqueous or non-aqueoussalt solution (as described below);

optionally, contacting each of the two or more opposingelectrically-conductive silver metal-containing patterns with an aqueousor non-aqueous non-salt solution (as described below); and

optionally, drying each of the two or more opposingelectrically-conductive silver metal-containing patterns. Such dryingcan be carried out using any suitable drying conditions and equipment,for example as described above for other drying operations.

When such a method is carried out, all of the photosensitive thin filmpatterns on both the first supporting side and the second opposingsupporting side of the continuous substrate, can be provided using thesame or different flexographic printing members.

Silver Conductivity Enhancement:

Once electrically-conductive metallic silver has been generated in aproduct article as described above, its electrical conductivity can beenhanced in some embodiments using one or more (or even two or more)treatment cycles comprising contact of the product article with anaqueous or non-aqueous salt solution containing a salt (as describedbelow) followed by drying the product article. Thus, such treatmentcycles are optional but when they are used, each of these two-steptreatment cycle comprises two essential features: (1) contacting theelectrically-conductive silver metal in the product article with theaqueous or non-aqueous salt solution, and (2) optionally, drying theelectrically-conductive silver metal in the product article (forexample, as described above for other drying operations). It isparticularly useful for the method according to this invention tocomprise two or more additional two-step treatment cycles beyond thefirst two-step treatment cycle, with drying after each contacting stepin each two-step treatment cycle, to enhance the electrical conductivityof the silver metal in the product article provided according to thisinvention. The result of these processes is the provision of “treatedsilver metal” in the product article.

Each two-step treatment cycle can be carried out using the same ordifferent aqueous or non-aqueous salt solution. Thus, the same ordifferent salts can be used in the multiple two-step treatment cycles,but in most embodiments where multiple two-step treatment cycles areused, the same salt is used in each two-step treatment cycle. Usefulsalts are described below.

As used herein for the treatment cycles, the term “aqueous” means thatthe solution (whether salt solution or non-salt solution) compriseswater as the predominant solvent among the total solvents in thesolution. That means that greater than 60 volume % of the total volumeof solvents is composed of water. Generally, such aqueous solutionscomprise water in an amount of at least 90 volume % of total solvents.

As used herein for the treatment cycles, the term “non-aqueous” meansthat the solution (whether salt solution or non-salt solution) comprisesone or more organic solvents (described below) as the predominantsolvent(s) among the total solvents in the solution. That means thatgreater than 60 volume % of the total volume of solvents is composed ofone or more organic solvents. Generally, such non-aqueous solutionscomprise one or more organic solvents in an amount of at least 90 volume% of total solvents.

Each treatment cycle can further include an additional contacting stepwhereby the silver metal is contacted with an aqueous or non-aqueousnon-salt solution (that does not contain any salts described for theaqueous or non-aqueous salt solutions) after contacting the productarticle with the aqueous or non-aqueous salt solution but before dryingthe product article. Such aqueous or non-aqueous non-salt solutions canbe composed predominantly of water. Alternatively, the non-saltsolutions can be comprised of predominantly one or more organic solventsas described below and thus be non-aqueous non-salt solutions.

The use of a non-salt aqueous or non-aqueous solution contacting step isnot essential, but it can be very desirable in many embodiments. Thus,such a three-step treatment cycle would include (1) contacting theproduct article with an aqueous or non-aqueous salt solution, (la)contacting the product article with an aqueous or non-aqueous non-saltsolution (such as plain water), and (2) optionally, drying the productarticle (using conditions described above). Each of these three-steptreatment cycles can be used multiple times, or only one time along withone or more of the two-step treatment cycles described above.

In each two-step or three-step treatment cycle, the product article canbe contacted with an aqueous or non-aqueous salt solution in anysuitable manner, such as by spraying, coating, immersion into a bath, oranother contacting means that would be readily apparent to one skilledin the art. The aqueous or non-aqueous salt solution is generally usedat a temperature of at least 20° C. or at least 30° C. and up to andincluding 90° C., or at least 45° C. and up to and including 80° C., oreven at least 40° C. and up to and including 70° C. The temperature canbe the same or different for each of the treatment cycles. Thetemperature can be adjusted for a given type of aqueous or non-aqueoussolution and depending upon whether a salt is present or not.

Contacting with an aqueous or non-aqueous non-salt solution in athree-step treatment cycle can be carried out within the sametemperature ranges using the same or different contacting means, but thetemperature need not be the same as that used for the aqueous ornon-aqueous salt solution in each three-step treatment cycle.

For each two-step or three-step treatment cycle, the noted contactingwith an aqueous or non-aqueous salt solution can be generally carriedout for at least 6 seconds and up to and including 30 minutes or morelikely for at least 30 seconds and up to and including 20 minutes, but aparticularly useful time for this contacting in at least one two-steptreatment cycle is at least 15 seconds and up to and including 1 minuteso that each two-step or three-step treatment cycle is relatively short.The contacting times for the multiple two-step or three-step treatmentcycles can be the same or different. However, in some embodiments, thecontacting time in the first two-step or three-step treatment cycle canbe longer than the contacting time in the successive two-step orthree-step treatment cycle(s).

The contacting steps in the three-step treatment cycles using theaqueous or non-aqueous non-salt solutions can be similarly carried outusing the times, temperatures, and contacting means described above forcontacting with the aqueous or non-aqueous salt solutions, but thetimes, temperatures, and contacting means need not be the same for eachtype of contacting, or for each two-step or three-step treatment cycle.

The drying operation for each two-step or three-step treatment cycle,when used, can be carried out using any suitable drying means, such asambient (unassisted) drying means, or active use of hot air orunassisted evaporation, and the drying time and temperature can bereadily determined with routine experimentation (other conditionsdescribed above). The drying means can be the same or different for eachtwo-step or three-step treatment cycle.

Useful salts for the aqueous salt solutions used in the same ordifferent two-step or three-step treatment cycles include but are notlimited to, one or more chloride salts (such as sodium chloride,potassium chloride, and ammonium chloride), bromide salts (such assodium bromide, potassium bromide, and ammonium bromide), silver salts(such as silver nitrate, silver acetate, and others known in the art).The salts can be used singly or in combination, and their totalconcentration in the aqueous salt solution is generally at least 0.1weight % and up to and including 20 weight %, or typically at least 1weight % and up to and including 10 weight %. Particularly useful saltsare the chloride salts, singly or in combination.

Useful salts for the non-aqueous salt solutions for the same ordifferent treatment cycles include but are not limited to, one or morechloride salts (such as tetrabutylammonium chloride), bromide salts(such as tetrabutylammonium bromide), silver salts (such as silvernitrate). The salt can be used singly or in combination, and their totalconcentration in the solvent salt solution is generally at least 0.1weight % and up to and including 20 weight %, or typically at least 1weight % and up to and including 10 weight %. Particularly useful saltsare the chloride salts, singly or in combination

Each aqueous salt solution or aqueous non-salt solution generally has apH of at least 4 and up to and including 11, or typically a pH of atleast 6 and up to and including 8. The pH can be adjusted using asuitable alkaline compound (such as a hydroxide) and any suitable buffercan be included to maintain the desired pH, as long as these additionalcomponents do not detract from the desired effect of enhancingelectrical conductivity of the silver metal in the product articles. Thenon-salt aqueous solutions can be plain water with nothing added, butthey can optionally include a surfactant, biocide, or buffer if desired.

Non-aqueous salt solutions and aqueous non-salt solutions contain one ormore organic solvents that include, but are not limited to,acetonitrile, butyronitrile, propionitrile, acetone, 2-butanone,methanol, ethanol, iso-propanol, and other similar organic solvents thatwould be readily apparent to one skilled in the art.

Thus, in some embodiments of the present invention, after a productarticle is provided using the photochemical reduction of reduciblesilver ions describe above, the product article can be subjected to twoor more two-step or three-step treatment cycles wherein each two-step orthree-step treatment cycle includes essential steps (1) and (2)described above, but each three-step treatment cycle includes step (la)described above. Each contacting step (1) can be carried out for atleast 1 second and up to and including 60 seconds at a temperature notedabove, with one or more salts having a total salt concentration of atleast 0.01 mol/l and up to and including 0.5 mol/l, and contacting step(la) can be carried out for a similar time particularly using plainwater.

In some embodiments, after a product article is provided using thephotochemical reduction of reducible silver ions describe above, theproduct article containing silver metal can be sprayed with water, or anaqueous or non-aqueous salt solution followed by suitable drying.

In other embodiments once the metallic silver is formed, the productarticle can be contacted with (1) a non-aqueous salt-containingsolution, and (2) optional drying. It is particularly desired to use twoor more additional two-step treatment cycles beyond this first two-steptreatment cycle to enhance the electrical conductivity of the silvermetal in the product article.

Moreover, as described above, each two-step treatment cycle can beconverted into a three-step treatment cycle to include (I a) contactingthe silver metal with an aqueous or non-aqueous non-salt aqueoussolution before any drying.

Thus, after photochemically converting the reducible silver ions tosilver metal, the method can include contacting theelectrically-conductive silver metal-containing thin film orelectrically-conductive silver metal-containing thin film pattern withwater or an aqueous or non-aqueous salt solution, and optionally, dryingthe silver metal-containing thin film or silver metal-containing thinfilm pattern.

Alternatively, the method according to this invention, comprises: afterphotochemically converting the reducible silver ions to silver metal,contacting the electrically-conductive silver metal-containing thin filmor electrically-conductive silver metal-containing thin film patternwith water or an aqueous or non-aqueous non-salt solution, and

optionally, drying the electrically-conductive silver metal-containingthin film or electrically-conductive silver metal-containing thin filmpattern.

In other embodiments, the method according to the present invention,comprises:

after photochemically converting the reducible silver ions to silvermetal, contacting the electrically-conductive silver metal-containingthin film or electrically-conductive silver metal-containing thin filmpattern with an aqueous or non-aqueous salt solution,

contacting the electrically-conductive silver metal-containing thin filmor electrically-conductive silver metal-containing thin film patternwith water of an aqueous or non-aqueous non-salt solution, and

optionally, drying the electrically-conductive silver metal-containingthin film or electrically-conductive silver metal-containing thin filmpattern.

The present invention provides at least the following embodiments andcombinations thereof, but other combinations of features are consideredto be within the present invention as a skilled artisan would appreciatefrom the teaching of this disclosure:

1. A photosensitive reducible silver ion-containing compositioncomprising:

a) a non-hydroxylic-solvent soluble silver complex comprising areducible silver ion complexed with an α-oxy carboxylate and a 5- or6-membered N-heteroaromatic compound,

the non-hydroxylic-solvent soluble silver complex being represented bythe following formula (I):

(Ag⁺)_(a)(L)_(b)(P)_(c)   (I)

wherein L represents the α-oxy carboxylate; P represents the 5- or6-membered N-heteroaromatic compound; a is 1 or 2; b is 1 or 2; and c is1, 2, 3, or 4, provided that when a is 1, b is 1, and when a is 2, b is2;

b) optionally, a photosensitizer that can either reduce the reduciblesilver ion or oxidize the α-oxy carboxylate; and

c) a solvent medium comprising at least one non-hydroxylic solvent.

2. The photosensitive reducible silver ion-containing composition ofembodiment 1, wherein the photosensitizer is present, and when thephotosensitizer is an electron-donating photosensitizer, it is definedby the following Equation 7, and when the photosensitizer is anelectron-accepting photosensitizer, it is defined by the followingEquation (4):

E _(S) *−E _(S) ^(ox) ≧−E _(Ag+) ^(red)  Equation (7)

E _(S) *+E _(S) ^(red) ≧E _(C) ^(ox)  Equation (4),

wherein:

E_(S) ^(ox) is the oxidation potential of the electron-donatingphotosensitizer;

E_(S)* is the excitation energy of the electron-acceptingphotosensitizer;

E_(S) ^(red) is the reduction potential of the electron-acceptingphotosensitizer;

E_(Ag+) ^(red) is the reduction potential of the silver ion in thenon-hydroxylic-solvent soluble silver complex; and

E_(C) ^(ox) is the oxidation potential of the α-oxy carboxylate.

3. The photosensitive reducible silver ion-containing composition ofembodiment 1 or 2, wherein one or more non-hydroxylic-solvent solublesilver complexes are present in an amount of at least 5 weight % and upto and including 90 weight % based on the total weight of thephotosensitive reducible silver ion-containing composition; and thephotosensitizer is present in an amount of at least 0.5 weight % and upto and including 4 weight %, based on the total weight of the one ormore non-hydroxylic-solvent soluble silver complexes.

4, The photosensitive reducible silver ion-containing composition of anyof embodiments 1 to 3, wherein the solvent medium comprises one or morenon-hydroxylic solvents selected from the group consisting ofacetonitrile, benzonitrile, acetone, methyl ethyl ketone, butyronitrile,propylene carbonate, propionitrile, isovaleronitrile, valeronitrile, anda mixture of two or more of these organic solvents.

5. The photosensitive reducible silver ion-containing composition of anyof embodiments 1 to 4, which meets a silver ion stability test such thatwhen the photosensitive reducible silver ion-containing composition isheld for 24 hours at ambient temperature and in yellow safelight, lessthan 0.1 mol % of its original silver ion content is reduced to silvermetal.

6. The photosensitive reducible silver ion-containing composition of anyof embodiments 1 to 5, wherein the photosensitizer is present as anelectron-accepting photosensitizer that is at least one of the followingcompounds PS-1 through PS-8:

E_(s)* E_(s) ^(red) PS-1

2.92 −0.91 PS-2

3.82 −1.88 PS-3

3.53 −0.7 PS-4

2.85 −0.4 PS-5

2.9 −0.4 PS-6

2.13 0.0 PS-7

2.53 −1.1 PS-8

3.1 −0.29

7. The photosensitive reducible silver ion-containing composition of anyof embodiments 1 to 5, wherein the photosensitizer is present as anelectron-donating photosensitizer and is at least one of the followingcompounds PS-9 through PS-18:

E_(s)* E_(s) ^(ox) PS-9 

3.2 0.98 PS-10

3.67 1.16 PS-11

2.43 1.77 PS-12

2.52 1.77 PS-13

NA NA PS-14

2.42 1.8 PS-15

2.42 1.8 PS-16

3.3 1.3 PS-17

3.3 1.3 PS-18

3.4 1.5 wherein NA means not available.

8. The photosensitive reducible silver ion-containing composition of anyof embodiments 1 to 7, wherein L is represented by the following formula(II):

wherein R₁, R₂, and R₃ are independently hydrogen or branched or linearalkyl groups.

9. The photosensitive reducible silver ion-containing composition ofembodiment 8, wherein R₁ is hydrogen or a branched or linear alkyl grouphaving 1 to 3 carbon atoms, and R₂ and R₃ are independently branched orlinear alkyl groups having 1 to 8 carbon atoms, wherein any of thehydrogen atoms in the R₁, R₂, and R₃ branched or linear alkyl groupsoptionally can be replaced with a fluorine atom.

10. The photosensitive reducible silver ion-containing composition ofany of embodiments 1 to 9, wherein the α-oxy carboxylate is selectedfrom the group consisting of lactic acid, 2-hydroxybutyric acid,2-hydroxy-3-methylbutyric acid, 2-hydroxy-3,3-dimethylbutyric acid,2-hydroxy-isobutyric acid, 2-hydroxy-2-methylbutyric acid,2-ethyl-2-hydroxybutyric acid, 2-hydroxy-2,3-dimethylbutyric acid,2-ethyl-2-methoxybutyric acid, 2-methoxy-2-methylpropanoic acid,1-hydroxycyclopentane-1-carboxylic acid,2,3-dihydroxy-2,3-dimethylsuccinic acid, and2,4-dihydroxy-2,4-dimethylpentanedioic acid, or

selected from the group consisting of pyruvic acid, 3-methylpyruvicacid, 3,3-dimethylpyruvic acid, 3,3-dimethyl-2-oxobutanoic acid,3,3-dimethyl-2-oxopentanoic acid, and 2,3-dioxosuccinic acid.

11. The photosensitive reducible silver ion-containing composition ofany of embodiments 1 to 10, wherein L is represented by the followingformula (III):

wherein R₄ is a branched or linear alkyl group having 1 to 8 carbonatoms and any of hydrogen atoms of the R₄ branched or linear alkyl groupoptionally can be replaced with a fluorine atom.

12. The photosensitive reducible silver ion-containing composition ofany of embodiments 1 to 11, wherein P is a 6-membered N-heteroaromaticcompound.

13. The photosensitive reducible silver ion-containing composition ofany of embodiments 1 to 12, wherein P is a 5- or 6-memberedN-heteroaromatic compound selected from the group consisting ofpyridine, 2-methylpyridine, 4-methylpyridine, 2,6-dimethylpyridine,2,3-dimethylpyridine, 3,4-dimethylpyridine, 4-pyridylacetone,3-chloropyridine, 3-fluoropyridine, oxazole, 4-methyloxazole, isoxazole,3-methylisoxazole, pyrimidine, pyrazine, pyridazine, and thiazole.

14. The photosensitive reducible silver ion-containing composition ofany of embodiments 1 to 13, wherein the 5- or 6-memberedN-heteroaromatic compound has an oxidation potential of at least 1.0 Vvs. SCE; the α-oxy carboxylate has a first oxidation potential of atleast 1.2 V vs. SCE; and upon decarboxylation of the α-oxy carboxylate,a second radical is generated that has an oxidation potential of lessthan 1.0 V vs. SCE.

15. The photosensitive reducible silver ion-containing composition ofany of embodiments 1 to 14, wherein the 5- or 6-memberedN-heteroaromatic compound has an oxidation potential of at least 1.5 Vvs. SCE.

16. The photosensitive reducible silver ion-containing composition ofany of embodiments 1 to 15, comprising two or more differentnon-hydroxylic-solvent soluble silver complexes.

17. The photosensitive reducible silver ion-containing composition ofany of embodiments 1 to 16, comprising two or more differentphotosensitizers.

18. The photosensitive reducible silver ion-containing composition ofany of embodiments 1 to 17, wherein:

the photosensitizer is present;

L has a molecular weight of 250 or less, and L is represented by eitherthe following formula (II) or (III):

wherein R₁ is hydrogen or an alkyl group having 1 or 2 carbon atoms, R₂and R₃ are independently branched or linear alkyl groups having 1 to 8carbon atoms, wherein any of the hydrogen atoms in the R₁, R₂, and R₃branched or linear alkyl groups optionally can be replaced with afluorine atom, and R₄ is a branched or linear alkyl group having 1 to 8carbon atoms wherein any of the hydrogen atoms optionally can bereplaced with a fluorine atom; and

P is a 5- or 6-membered N-heteroaromatic compound that is selected fromthe group consisting of pyridine, 2-methylpyridine, 4-methylpyridine,2,6-dimethylpyridine, 2,3-dimethylpyridine, 3,4-dimethylpyridine,4-pyridylacetone, 3-chloropyridine, 3-fluoropyridine, oxazole,4-methyloxazole, isoxazole, 3-methylisoxazole, pyrimidine, pyrazine,pyridazine, and thiazole.

19. The photosensitive reducible silver ion-containing composition ofany of embodiments 1 to 18, wherein:

(i) a and b are both 1 and c is 1 or 2;

(ii) a and b are both 2 and c is 2; or

(iii) a and b are both 2 and c is 4.

The following Examples are provided to illustrate the practice of thisinvention and are not meant to be limiting in any manner.

Most reagents and solvents used in the following Examples can beobtained from various commercial sources such as VWR, Sigma-AldrichChemical Co. (Milwaukee, Wis., USA) and Fisher Scientific (Pittsburgh,Pa., USA).

Comparative Example 1: Preparation of Silver Isobutyrate PyridineComplex

To a slurry of silver isobutyrate (1 g, 5.18 mmol) in acetonitrile (4ml), pyridine (0.41 g, 5.18 mmol) was added and the resulting reactionmixture was stirred at 25° C. until a clear solution was obtained. Theclear reaction solution was then stirred for 10 minutes and acetonitrilewas slowly removed at room temperature to obtain a white solid of thedesired silver isobutyrate pyridine complex that was characterized by ¹HNMR (CD₃CN).

Attempted Photochemical Generation of Electrically-Conductive SilverMetal Using Silver Isobutyrate Pyridine Complex:

The silver isobutyrate pyridine complex noted above (0.4 g) wasdissolved in acetonitrile (1 ml). Photosensitizer PS-7 (0.02 g; 2 weight%) was added into the resulting solution and dissolved at roomtemperature. The resulting photosensitive silver ion-containingcomposition was spin coated onto a glass plate substrate at 800 rpm andthe resulting precursor article with thin film on the glass substratewas exposed to UV light using a medium pressure Hg/Xe (1000 W) lamp. Thecolor of the thin film in the resulting precursor article changed fromcolorless to yellow within 210 seconds, indicating the formation ofsilver nanoparticles (UV/Vis absorption spectrum shows an absorption inthe 400-425 nm range typically associated with the presence of silvermetal). Upon further irradiation (60-120 s), the color of the thin filmprogressively changed from yellow to brown, indicating the formation oflarger size silver nanoparticles. The sheet resistivity of the resultingprinted metallic silver features was measured using a 4-point probedevice and found to be non-electrically conductive. The thin filmresistivity did not change after washing it with a brine (sodiumchloride) solution (0.1 molar) for 10 seconds.

This example demonstrates that upon UV irradiation, a photosensitivesilver ion-containing composition comprising a complex formed fromreducible silver ions, an alkyl carboxylate, and a 5- or 6-memberedN-heteroaromatic compound and a photosensitizer does not generateelectrically-conductive silver metal.

Inventive Example 1: Preparation of Silver Lactate 2,6-DimethylpyridineComplex

To a slurry of silver lactate (1.0 g, 5.076 mmol) in acetonitrile (4ml), 2,6-dimethylpyridine (0.54 g, 5.08 mmol) was added and the reactionmixture was stirred to obtain a clear reaction solution. The resultingreaction solution was stirred at 25° C. for 10 minutes and acetonitrilewas slowly removed at room temperature to obtain a white solid of thedesired silver lactate 2,6-dimethylpyridine complex having the crystalstructure as shown in FIG. 1 and confirmed by ¹H NMR (CD₃CN).

Inventive Example 2: Preparation of Silver Lactate2,4,6-Trimethylpyridine Complex

To a slurry of silver lactate (1.0 g, 5.08 mmol) in acetonitrile (5 ml),2,4,6-trimethylpyridine (0.609 g, 5.08 mmol) was added and the resultingreaction solution was stirred at 25° C. for 10 minutes. The acetonitrilewas slowly removed at room temperature to obtain a white solid of thedesired silver lactate 2,4,6-dimethylpyridine complex having the crystalstructure as shown in FIG. 2 and confirmed by ¹H NMR (CD₃CN).

Inventive Example 3: Preparation of Silver Lactate 3-ChloropyridineComplex

To a slurry of silver lactate (1.0 g, 5.08 mmol) in acetonitrile (5 ml),3-chloropyridine (1.72 g, 15.24 mmol) was added and the resultingreaction solution was stirred at 25° C. for 10 minutes. The acetonitrilewas slowly removed at room temperature to obtain a white solid of thedesired silver lactate 3-chloropyridine complex as confirmed by ¹H NMR(CD₃CN).

Inventive Example 4: Preparation of Silver 2-Hydroxyisobutyrate PyridineComplex

Silver 2-hydroxyisobutyrate was prepared as follows. A solution of 50%sodium hydroxide solution (58.8 g; 0.735 moles) was added to 1.05 literof chilled (15° C.) deionized (DI) water employing mechanical stirringand external cooling at 15° C. 2-Hydroxyisobutyric acid (78.1 g; 0.750moles) was added in portions, maintaining the resulting reactionsolution temperature near or below ambient temperature. After thisaddition, the homogenous reaction solution was stirred at 15° C. for 30minutes to insure complete reaction. Silver nitrate (127.4 g; 0.75 mole)in deionized water (187.5 ml) was slowly added to the sodium2-hydroxyisobutyrate solution over 10 minutes. During the addition, aprecipitate formed. The reaction solution was stirred at 15° C. for 30minutes, and the slurry was filtered (medium frit size 90) and washedwith water (50 ml). The collected solid was further washed with two 200ml portions of acetone and air dried to provide the desired product ofsilver 2-hydroxyisobutyrate at 60% yield.

To a slurry of the formed silver 2-hydroxyisobutyrate (1 g, 4.76 mmol)in acetonitrile (5 ml), pyridine (0.75 g, 9.52 mmol) was added to obtaina clear reaction solution that was stirred for an additional 10-15minutes at 25° C. and the acetonitrile was slowly removed at roomtemperature to obtain a white solid of the desired silver2-hydroxyisobutyrate pyridine complex as confirmed by ¹H NMR (CD₃CN) δ8.56 (m, 2H), 7.8 (m, 1H), 7.4 (m. 2H), 1.40 (s, 6H).

Inventive Example 5: Preparation of Silver 2-Hydroxyisobutyrate2,6-Dimethylpyridine Complex

To a slurry of silver 2-hydroxyisobutyrate (1.0 g, 4.76 mmol) inacetonitrile (5 ml), 2,6-dimethylpyridine (1.01 g, 9.52 mmol) was addedto obtain a clear reaction solution that was then stirred for additional10-15 minutes at 25° C. and the acetonitrile was slowly removed at roomtemperature to obtain a white solid of the desired silver2-hydroxyisobutyrate pyridine complex as confirmed by ¹H NMR (CD₃CN) δ7.6 (m, 1H), 6.9 (m, 2H), 2.5 (s 6H), 1.40 (s, 6H).

Inventive Example 6: Preparation of Silver 2-Ethyl-2-HydroxybutyratePyridine Complex

Silver 2-ethyl-2-hydroxybutyrate was prepared as follows. A solution of50% sodium hydroxide solution (58.8 g; 0.735 moles) is added to 1.05liter chilled (15° C.) deionized (DI) water employing mechanicalstirring and external cooling at 15° C. 2-Ethyl-2-ethyl-2-hydroxybutyricacid (97.02 g; 0.750 moles) was added in portions maintaining theresulting reaction solution temperature near or below ambienttemperature. After this addition, the homogenous mixture is stirred at15° C. for 30 minutes to insure complete reaction. Silver nitrate (127.4g; 0.75 mole) in deionized water (187.5 ml) was slowly added to thesodium 2-hydroxyisobutyrate solution over 10 minutes. During theaddition, a precipitate formed. The reaction solution was stirred at 15°C. for 30 minutes, slurry filtered (medium frit size 90), and washedwater (50 ml). The collected solid was further washed with two 200 mlportions of acetone and air dried to provide the desired silver2-ethyl-2-hydroxybutyrate product at 60% yield.

To a slurry of silver 2-ethyl-2-hydroxybutyrate (1.0 g, 4.18 mmol) inacetonitrile (5 ml), pyridine (0.661 g, 8.37 mmol) was added and thereaction solution was stirred at 25° C. for 10 minutes. The acetonitrilewas slowly removed at room temperature to obtain a white solid of thedesired silver 2-ethyl-2-hydroxyisobutyrate pyridine complex having thecrystal structure shown in FIG. 3 as confirmed by ¹H NMR (CD₃CN).

Inventive Example 7: Preparation of Silver 2-Hydroxyisobutyrate OxazoleComplex

To a slurry of silver 2-hydroxyisobutyrate (1.0 g, 4.76 mmol) inacetonitrile (4 ml), oxazole (0.50 g, 19.2 mmol) was added to obtain aclear reaction solution. The reaction solution was stirred at 25° C. for10 minutes to obtain the desired silver 2-hydroxyisobutyrate oxazolecomplex as confirmed by ¹H NMR (CD₃CN) δ 8.08 (s, 1H), 7.90 (s, 1H),7.21 (s. 1H), 1.2 (s, 6H).

Inventive Example 8: Preparation of Silver Lactate 3-FluoropyridineComplex

To a slurry of silver lactate (1.0 g, 5.08 mmol) in acetonitrile (5 ml),3-fluoropyridine (1.97 g, 20.3 mmol) was added to obtain a clearreaction solution that was stirred at 25° C. for 10 minutes and thedesired silver lactate 3-fluoropyridine complex was characterized by 1HNMR (CD₃CN) δ 8.27 (d, 1H), 8.39 (d, 1H), 7.46 (d, 1H), 7.30 (d 1H), 4(q, 1H), 1.35 (d, 3H).

Inventive Example 9: Preparation of Silver 2-Hydroxyisobutyrate3-Fluoropyridine Complex

To a slurry of silver 2-hydroxyisobutyrate (1.0 g, 4.18 mmol) inacetonitrile (5 ml), 3-fluoropyridine (1.62 g, 16.72 mmol) was added toobtain a clear reaction solution that was stirred at 25° C. for 10minutes to obtain the desired silver 2-hydroxyisobutyrate3-fluoropyridine complex, the structure of which was confirmed by ¹H NMR(CD₃CN) δ 8.25 (d, 1H), 8.35 (d, 1H), 7.4 (d, 1H), 7.3 (d 1H), 1.35 (d,6H).

Inventive Example 10: Preparation of Silver 2-Hydroxyisobutyrate2-Methylpyrimidine Complex

To a slurry of silver 2-hydroxyisobutyrate (1.0 g, 4.76 mmol) inacetonitrile (4 ml), 2-methylpyrimidine (1.8 g, 19.2 mmol) was added toobtain a clear reaction solution that was stirred at 25° C. for 10minutes to obtain the desired silver 2-hydroxyisobutyrate2-methylpyrimidine complex the structure of which was confirmed by ¹HNMR analysis.

Inventive Example 11: Electrochemical Characterization of Silver-ionComplexes

The electrochemical properties of various silver-containing complexes asdefined above using formula (I) were assessed by the common method ofcyclic voltammetry as described for example in “Electrochemical Methods,Fundamentals and Applications”, A. Bard and L. Faulkner (Editors), JohnWiley & Sons, Inc. NY (1980). In this method, each complex was dissolvedat a concentration of about 1 to about 5 mmol in acetonitrile solventcontaining 0.1 molar tetrabutylammonium-tetrafluoroborate as anelectrolyte. Cyclic voltammetry was performed in a two-compartment glasscell equipped with a glassy carbon working electrode, a platinum counterelectrode, and a saturated calomel (SCE) reference electrode. The SCEwas separated from the main compartment of the cell by a salt bridgefilled with 0.1 molar tetrabutylammonium-tetrafluoroborate electrolyte.The glassy carbon electrode was polished using 1 μm alumina paste priorto each voltammetric scan. Measurements were conducted at 25° C. using apotential sweep rate of 0.1 V/sec.

A typical cyclic voltammogram of the silver 2-hydroxyisobutyratepyridine complex prepared in Inventive Example 4 is shown in FIG. 4wherein, the electrode potential is cycled between the limits of −0.5 Vand +2.0 V starting in a negative-going direction from an initialpotential of +0.5 V. Three electrochemically active regions wereidentified. The observed current “wave” in the negative potential regionfrom +0.1 V to −0.5 V is associated with the electrochemical reductionof the silver ion-containing complex. This reduction process results inthe plating of silver metal onto the carbon electrode. The sharp currentwave observed in the positive potential region from +0.1 V to +0.5 Vcorresponds to the oxidation of the plated silver metal to form solublesilver ion. The sharp symmetrical shape of the latter electrochemicaloxidation wave is fully consistent with the oxidation dissolution(“stripping”) of silver metal from the electrode surface. Finally, athird, broad electrochemical wave in the positive potential region fromabout +1.0 V to +2.0 V is assigned to the overlapping oxidation waves ofthe incorporated component parts (“P” and “L”) of the complex.

Cyclic voltammograms for other complexes of formula (I) are very similarto that of FIG. 4 Peak potentials for the reduction and oxidation ofvarious complexes are shown in TABLE III below. Oxidation potentialsdetermined for the individual α-oxy carboxylate components determined bythe experimental method described above are shown in the following TABLEIV. Oxidation potentials for primary alkylamines are found for examplein Adenier et al., Langmuir, 2004, Vol. 20, pp. 8243-8253.

TABLE III Voltammetry Results for (Ag⁺)_(a)(L)_(b)(P)_(c) inAcetonitrile Reduction Oxidation peak peak Complex L P StructurePotential Potential Comparative Example 1 iso-butyl acetate pyridine

 −0.27 V +1.07 V Inventive Example 1 lactate 2,6- dimethyl pyridine

 −0.21 V +1.32 V Inventive Example 4 hydroxy isobutyl- rate pyridine

+0.017 V +1.13 V lactate pyridine

+0.064 V +1.21 V

TABLE IV Voltammetry Results for Carboxylate Components in AcetonitrileOxidation L Peak Potential lactate  +1.1 V acetate +1.27 V

Inventive Example 12: Preparation of Silver 2-MethoxyisobutyratePyridine Complex

2-Methoxyisobutyric acid was synthesized as follows. A solution ofmethyl 2-hydroxyisobutyrate (2.0 g, 16.93 mmol) in N,N-dimethylformamide(20 ml) at 0° C. was treated with NaH (60% in mineral oil, 0.813 g,20.33 mmol), stirred for 30 minutes at 0° C., treated with iodomethane(1.269 ml, 20.29 mmol), allowed to warm to room temperature, and stirredovernight. The resulting solution was diluted with ethyl acetate,quenched with cold saturated ammonium chloride, and extracted with ethylacetate three times, and the combined organic extractions were washedwith saturated NaHCO₃, 10% lithium chloride, and sodium chloride, driedover sodium sulfate, and concentrated to dryness to afford 2-methoxyiso-butyrate sodium salt (2.08 g, 93% yield) as characterized by ¹H NMR(400 MHz, DMSO-d₆): δ 3.64 (s, 3H), 3.11 (s, 3H), 1.30 (s, 6H).2-Methoxy iso-butyrate silver salt was obtained by following methoddescribed above in Inventive Example 6.

Silver 2-methoxyisobutyrate pyridine complex was then prepared asfollows. To a slurry of silver 2-methoxy-isobutyrate as described above(1 g, 4.76 mmol) in acetonitrile (4 ml), pyridine (1.8 g, ˜23 mmol) wasadded to obtain a clear reaction solution that was stirred at 25° C. for10 minutes to obtain the desired silver 2-methoxyisobutyrate pyridinecomplex as confirmed by ¹H NMR analysis.

Inventive Example 13: Preparation of Silver Pyruvate Pyridine Complex

To a solution of pyruvic acid (1.0 g, 11.36 mmol) in acetonitrile (4ml), pyridine (1.8 g, 23 mmol) was added followed by addition of silvernitrate (1.93 g, 11.37 mmol). The resulting reaction solution wasstirred at 25° C. for 10 minutes to obtain the desired silver pyruvatepyridine complex as confirmed by ¹H NMR.

Inventive Example 14: Preparation of Silver 3-Methyl-2-oxobutanoatePyridine Complex

To a solution of 3-methyl-2-oxobutanoic acid (1.0 g, 8.62 mmol) inacetonitrile (4 ml), pyridine 1.5 g, 18 mmol) was added followed byaddition of silver nitrate (1.46 g, 8.62 mmol). The resulting reactionsolution was stirred at 25° C. for 10 minutes to obtain the desiredsilver 3-methyl-2-oxobutanate pyridine complex as confirmed by ¹H NMR.

Inventive Example 15: Preparation of Silver Lactate 4-MethylpyrimidineComplex

To a slurry of silver lactate (1.0 g, 5.1 mmol) in acetonitrile (4 ml),oxazole (1.84 g, 20.2 mmol) was added to obtain a clear reactionsolution that was stirred at 25° C. for 10 minutes to obtain the desiredsilver lactate 4-methylpyrimidine complex as confirmed by ¹H NMR (CD₃CN)δ 9.06 (s, 1H), 8.61 (d, 1H), 7.37 (d, 1H), 4 (q, 1H), 2.54 (s, 3H),1.35 (d, 3H).

Inventive Example 16: Printing and Photochemical Generation ofConductive Silver Metal Using 2-Hydroxyisobutyrate Pyridine Complex andPS-7 Electron Donor Photosensitizer

This example demonstrates the preparation of precursor articlesaccording to the present invention using flexographic printing and asilver ion-containing complex described below. It also demonstrates thephotochemical generation, using the coumarin class of electron donorphotosensitizers, of electrically-conductive silver metal in suchprecursor articles to provide product articles comprising polymericsubstrates.

A flexographic printing plate was obtained from a commercially availableKodak Flexcel NX photopolymer plate (precursor) using a flexographic IGTF printer. A relief image was provided by imaging the photopolymer platethrough a mask that was written using the Kodak Square Spot lasertechnology at a resolution of 12,800 dpi. Exposure was carried out usinga Fusion benchtop conveyor unit equipped with H-bulb at a nominal UVdose of between 100-500 mJ/cm².

The silver 2-hydroxyisobutyrate pyridine complex described above inInventive Example 4 (0.4 g) was dissolved in acetonitrile (1 ml).Photosensitizer PS-7 (0.02 g; 2 weight %) was added and dissolved toform the resulting photosensitive reducible silver ion-containingcomposition at room temperature. Test patterns of this composition wereprinted onto samples of a gelatin-subbed poly(ethylene terephthalate)(PET) film substrate to provide a precursor article with photosensitivethin film patterns on the substrate. The precursor article was exposedto UV light to obtain thin film silver metal patterns in a productarticle. Each sample product article was contacted (for about 10-30seconds and 40° C.) with a sodium chloride solution (0.1-0.2 molar) andair dried before measuring the sheet resistivity of the resulting silvermetal patterns using a 4-point probe device, which was found to be7-10Ω/□. The resistivity was measured by a four-point probe for thefilms with a 0.5×1.5 cm area and nominal thickness of 400 nm. Thesurface morphology and the thickness of the silver films were observedby scanning electron microscopy (SEM).

Inventive Example 17: Printing and Photochemical Generation ofConductive Silver Metal Using Silver 2-Hydroxyisobutyrate OxazoleComplex

A flexographic printing plate was obtained from a commercially availableKodak Flexcel NX photopolymer plate (precursor) using a flexographic IGTF1 printer. A relief image was provided by imaging the photopolymerplate through a mask that was written using the Kodak Square Spot lasertechnology at a resolution of 12,800 dpi. Exposure was carried out usinga Fusion benchtop conveyor unit equipped with H-bulb at a nominal UVdose of 500 to 1000 mJ/cm².

The silver 2-hydroxyisobutyrate oxazole complex described above inInventive Example 7 (0.4 g) was dissolved in acetonitrile (1 ml).Photosensitizer PS-7 (0.02 g; 2 weight %) was added and dissolved toform a photosensitive reducible silver ion-containing composition atroom temperature. Test patterns of this composition were printed onsamples of a gelatin-subbed poly(ethylene terephthalate) (PET) filmsubstrate to provide a precursor article with photosensitive thin filmpatterns on the substrate. The precursor article was exposed to UV lightto obtain thin film silver metal patterns. The surface morphology andthe thickness of the silver metal thin film were observed by scanningelectron microscopy (SEM). The resistivity was measured by a four-pointprobe device for each pattern over a 0.5×1.5 cm area and nominalthickness of 400 nm. The sheet resistivity of the resulting silver metalthin film pattern in the product article was 30-50Ω/□.

The resistivity of the sample significantly decreased after contactingthe product article with an aqueous salt solution for about 10-30seconds and at 40° C. with a sodium chloride solution (0.1-0.2 molar)and air dried before measuring the sheet resistivity of the resultingsilver metal patterns in the product article using a 4-point probedevice, which was found to be 11 fl/o.

Inventive Example 18: Ink-Jet Printing and Photochemical Generation ofConductive Silver Metal Using Silver 2-Hydroxyisobutyrate PyridineComplex and PS-12 Electron Donor Photosensitizer

The inventive photosensitive reducible silver ion-containing compositioncontaining the silver 2-hydroxyisobutyrate pyridine complex and PS-12electron donating photosensitizer was printed by an ink-jet printer ontovarious plastic substrates. The printer setup consisted of adrop-on-demand (DOD) piezoelectric ink-jet nozzle manufactured fromMicrofab Technologies, Inc. (Plano, Tex.) with a 60 μm orifice. Theprint head was mounted onto a computer-controlled three-axis gantrysystem capable of a movement accuracy of ±5 μm. The gap between thenozzle and the surfaces was maintained at −2 mm during printing at 25°C. and 40% relative humidity. Uniform ejection of the compositiondroplets was performed by applying 40 V impulse lasting 25 μs at afrequency of 800 Hz. A charge coupled device (CCD) camera equipped witha strobe light emitting diode (LED) light was employed to watchindividual droplets by which their physical properties were analyzed.

Various patterns a 40 weight % solution of silver 2-hydroxyisobutyratepyridine complex (from Inventive Example 4) comprising 2 weight % (withrespect to the complex) of PS-12 photosensitizer, were printed onflexible polymeric polyethylene terephthalate (PET) substrate. In onesample, a line pattern was generated by narrowing the dot-to-dotdistance. The resulting patterns were exposed to UV light using a mediumpressure Hg/Xe light source (1000 W, nominal UV dose of 500-1000 mJ/cm²)followed by contacting the resulting product article with a sodiumchloride solution (0.1-0.2 molar) and air dried before measuringresistivity. Resistance of a 0.35 mm×15 mm (300 nm thick) printed linewas measured using a commercially available multimeter and found to be950Ω. For a 0.35 mm×5 mm line resistance was 250Ω.

Inventive Example 19: Printing and Photochemical Generation ofConductive Silver Metal Using 2-Hydroxyisobutyrate Pyridine Complex andPS-4 Electron Acceptor Photosensitizer

This example demonstrates the photochemical generation ofelectrically-conductive silver metal in precursor articles to provideproduct articles comprising a polymeric substrate, using an acridiniumclass electron accepting photosensitizer.

The silver 2-hydroxyisobutyrate pyridine complex described above inInventive Example 4 (0.4 g) was dissolved in a mixture of acetonitrileand butyronitrile (1 ml; 85:15 v/v). Photosensitizer PS-4 (0.02 g; 2weight %) was added and dissolved to form the resulting photosensitivereducible silver ion-containing composition at room temperature. Testpatterns of this composition were printed using a flexographic printingplate on samples of a gelatin-subbed poly(ethylene terephthalate) (PET)film substrate to provide a precursor article with photosensitive thinfilm patterns on the substrate. The precursor article was exposed to UVlight to obtain thin film silver metal patterns in a resulting productarticle. Each sample was contacted (for about 10-30 seconds and 40° C.)with a sodium chloride solution (0.1-0.2 molar) and air dried beforemeasuring the sheet resistivity. The resistivity measured by afour-point probe for the films with a 0.5×1.5 cm area and nominalthickness of 400 nm was found to be 10-15Ω/□.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

1. A photosensitive reducible silver ion-containing compositioncomprising: a) a non-hydroxylic-solvent soluble silver complexcomprising a reducible silver ion complexed with an α-oxy carboxylateand a 5- or 6-membered N-heteroaromatic compound, thenon-hydroxylic-solvent soluble silver complex being represented by thefollowing formula (I):(Ag⁺)(L)_(b)(P)_(c)   (I) wherein L represents the α-oxy carboxylate; Prepresents the 5- or 6-membered N-heteroaromatic compound; a is 1 or 2;b is 1 or 2; and c is 1, 2, 3, or 4, provided that when a is 1, b is 1,and when a is 2, b is 2; b) optionally, a photosensitizer that caneither reduce the reducible silver ion or oxidize the α-oxy carboxylate;and c) a solvent medium comprising at least one non-hydroxylic solvent.2. The photosensitive reducible silver ion-containing composition ofclaim 1, wherein the photosensitizer is present, and when thephotosensitizer is an electron-donating photosensitizer, it is definedby the following Equation 7, and when the photosensitizer is anelectron-accepting photosensitizer, it is defined by the followingEquation (4):E _(S) *−E _(S) ^(ox) ≧−E _(Ag+) ^(red)  Equation (7)E _(S) *+E _(S) ^(red) ≧E _(C) ^(ox)  Equation (4), wherein: E_(S) ^(ox)is the oxidation potential of the electron-donating photosensitizer;E_(S)* is the excitation energy of the electron-acceptingphotosensitizer; E_(S) ^(red) is the reduction potential of theelectron-accepting photosensitizer; E_(Ag+) ^(red) is the reductionpotential of the silver ion in the non-hydroxylic-solvent soluble silvercomplex; and E_(C) ^(ox) is the oxidation potential of the α-oxycarboxylate.
 3. The photosensitive reducible silver ion-containingcomposition of claim 1, wherein one or more non-hydroxylic-solventsoluble silver complexes are present in an amount of at least 5 weight %and up to and including 90 weight % based on the total weight of thephotosensitive reducible silver ion-containing composition; and thephotosensitizer is present in an amount of at least 0.5 weight % and upto and including 4 weight %, based on the total weight of the one ormore non-hydroxylic-solvent soluble silver complexes.
 4. Thephotosensitive reducible silver ion-containing composition of claim 1,wherein the solvent medium comprises one or more non-hydroxylic solventsselected from the group consisting of acetonitrile, benzonitrile,acetone, methyl ethyl ketone, butyronitrile, propylene carbonate,propionitrile, isovaleronitrile, valeronitrile, and a mixture of two ormore of these organic solvents.
 5. The photosensitive reducible silverion-containing composition of claim 1 that meets a silver ion stabilitytest such that when the photosensitive reducible silver ion-containingcomposition is held for 24 hours at ambient temperature and in yellowsafelight, less than 0.1 mol % of its original silver ion content isreduced to silver metal.
 6. The photosensitive reducible silverion-containing composition of claim 1, wherein the photosensitizer ispresent as an electron-accepting photosensitizer that is at least one ofthe following compounds PS-1 through PS-8: E_(s)* E_(s) ^(red) PS-1

2.92 −0.91 PS-2

3.82 −1.88 PS-3

3.53 −0.7 PS-4

2.85 −0.4 PS-5

2.9 −0.4 PS-6

2.13 0.0 PS-7

2.53 −1.1 PS-8

3.1 −0.29


7. The photosensitive reducible silver ion-containing composition ofclaim 1, wherein the photosensitizer is present as an electron-donatingphotosensitizer and is at least one of the following compounds PS-9through PS-18: E_(s)* E_(s) ^(ox) PS-9 

3.2 0.98 PS-10

3.67 1.16 PS-11

2.43 1.77 PS-12

2.52 1.77 PS-13

NA NA PS-14

2.42 1.8 PS-15

2.42 1.8 PS-16

3.3 1.3 PS-17

3.3 1.3 PS-18

3.4 1.5 wherein NA means not available.


8. The photosensitive reducible silver ion-containing composition ofclaim 1, wherein L is represented by the following formula (II):

wherein R₁, R₂, and R₃ are independently hydrogen or branched or linearalkyl groups.
 9. The photosensitive reducible silver ion-containingcomposition of claim 8, wherein R₁ is hydrogen or a branched or linearalkyl group having 1 to 3 carbon atoms, and R₂ and R₃ are independentlybranched or linear alkyl groups having 1 to 8 carbon atoms, wherein anyof the hydrogen atoms in the R₁, R₂, and R₃ branched or linear alkylgroups optionally can be replaced with a fluorine atom.
 10. Thephotosensitive reducible silver ion-containing composition of claim 1,wherein the α-oxy carboxylate is selected from the group consisting oflactic acid, 2-hydroxybutyric acid, 2-hydroxy-3-methylbutyric acid,2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-isobutyric acid,2-hydroxy-2-methylbutyric acid, 2-ethyl-2-hydroxybutyric acid,2-hydroxy-2,3-dimethylbutyric acid, 2-ethyl-2-methoxybutyric acid,2-methoxy-2-methylpropanoic acid, 1-hydroxycyclopentane-1-carboxylicacid, 2,3-dihydroxy-2,3-dimethylsuccinic acid, and2,4-dihydroxy-2,4-dimethylpentanedioic acid, or selected from the groupconsisting of pyruvic acid, 3-methylpyruvic acid, 3,3-dimethylpyruvicacid, 3,3-dimethyl-2-oxobutanoic acid, 3,3-dimethyl-2-oxopentanoic acid,and 2,3-dioxosuccinic acid.
 11. The photosensitive reducible silverion-containing composition of claim 1, wherein L is represented by thefollowing formula (III):

wherein R₄ is a branched or linear alkyl group having 1 to 8 carbonatoms and any of hydrogen atoms of the R₄ branched or linear alkyl groupoptionally can be replaced with a fluorine atom.
 12. The photosensitivereducible silver ion-containing composition of claim 1, wherein P is a6-membered N-heteroaromatic compound.
 13. The photosensitive reduciblesilver ion-containing composition of claim 1, wherein P is a 5- or6-membered N-heteroaromatic compound selected from the group consistingof pyridine, 2-methylpyridine, 4-methylpyridine, 2,6-dimethylpyridine,2,3-dimethylpyridine, 3,4-dimethylpyridine, 4-pyridylacetone,3-chloropyridine, 3-fluoropyridine, oxazole, 4-methyloxazole, isoxazole,3-methylisoxazole, pyrimidine, pyrazine, pyridazine, and thiazole. 14.The photosensitive reducible silver ion-containing composition of claim1, wherein the 5- or 6-membered N-heteroaromatic compound has anoxidation potential of at least 1.0 V vs. SCE; the α-oxy carboxylate hasa first oxidation potential of at least 1.2 V vs. SCE; and upondecarboxylation of the α-oxy carboxylate, a second radical is generatedthat has an oxidation potential of less than 1.0 V vs. SCE.
 15. Thephotosensitive reducible silver ion-containing composition of claim 1,wherein the 5- or 6-membered N-heteroaromatic compound has an oxidationpotential of at least 1.5 V vs. SCE.
 16. The photosensitive reduciblesilver ion-containing composition of claim 1, comprising two or moredifferent non-hydroxylic-solvent soluble silver complexes.
 17. Thephotosensitive reducible silver ion-containing composition of claim 16,comprising two or more different photosensitizers.
 18. Thephotosensitive reducible silver ion-containing composition of claim 1,comprising two or more different photosensitizers.
 19. Thephotosensitive reducible silver ion-containing composition of claim 1,wherein: the photosensitizer is present; L has a molecular weight of 250or less, and L is represented by either the following formula (II) or(III):

wherein R₁ is hydrogen or an alkyl group having 1 or 2 carbon atoms, R₂and R₃ are independently branched or linear alkyl groups having 1 to 8carbon atoms, wherein any of the hydrogen atoms in the R₁, R₂, and R₃branched or linear alkyl groups optionally can be replaced with afluorine atom, and R₄ is a branched or linear alkyl group having 1 to 8carbon atoms wherein any of the hydrogen atoms optionally can bereplaced with a fluorine atom; and P is a 5- or 6-memberedN-heteroaromatic compound that is selected from the group consisting ofpyridine, 2-methylpyridine, 4-methylpyridine, 2,6-dimethylpyridine,2,3-dimethylpyridine, 3,4-dimethylpyridine, 4-pyridylacetone,3-chloropyridine, 3-fluoropyridine, oxazole, 4-methyloxazole, isoxazole,3-methylisoxazole, pyrimidine, pyrazine, pyridazine, and thiazole. 20.The photosensitive reducible silver ion-containing composition of claim1, wherein: (i) a and b are both 1 and c is 1 or 2; (ii) a and b areboth 2 and c is 2; or (iii) a and b are both 2 and c is 4.